diff --git a/lib/doodstream-upload.js b/lib/doodstream-upload.js
index aac1baa..caafab7 100644
--- a/lib/doodstream-upload.js
+++ b/lib/doodstream-upload.js
@@ -210,7 +210,8 @@ class DoodstreamUploader {
     let preamble = '';
     preamble += `--${boundary}\r\nContent-Disposition: form-data; name="sess_id"\r\n\r\n${this.sessId}\r\n`;
     preamble += `--${boundary}\r\nContent-Disposition: form-data; name="utype"\r\n\r\nreg\r\n`;
-    preamble += `--${boundary}\r\nContent-Disposition: form-data; name="file"; filename="${fileName}"\r\nContent-Type: application/octet-stream\r\n\r\n`;
+    const safeFileName = fileName.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
+    preamble += `--${boundary}\r\nContent-Disposition: form-data; name="file"; filename="${safeFileName}"\r\nContent-Type: application/octet-stream\r\n\r\n`;
 
     const epilogue = `\r\n--${boundary}--\r\n`;
     const preambleBuf = Buffer.from(preamble, 'utf-8');
diff --git a/lib/hosters.js b/lib/hosters.js
index 4ddd685..80e2b49 100644
--- a/lib/hosters.js
+++ b/lib/hosters.js
@@ -232,7 +232,8 @@ function buildMultipart(filePath, formFields) {
     preamble += `${value}\r\n`;
   }
   preamble += `--${boundary}\r\n`;
-  preamble += `Content-Disposition: form-data; name="file"; filename="${fileName}"\r\n`;
+  const safeFileName = fileName.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
+  preamble += `Content-Disposition: form-data; name="file"; filename="${safeFileName}"\r\n`;
   preamble += `Content-Type: application/octet-stream\r\n\r\n`;
 
   const epilogue = `\r\n--${boundary}--\r\n`;
diff --git a/lib/vidmoly-upload.js b/lib/vidmoly-upload.js
index 54952df..2156fc2 100644
--- a/lib/vidmoly-upload.js
+++ b/lib/vidmoly-upload.js
@@ -200,7 +200,8 @@ class VidmolyUploader {
       preamble += `${value}\r\n`;
     }
     preamble += `--${boundary}\r\n`;
-    preamble += `Content-Disposition: form-data; name="${fileFieldName || 'file'}"; filename="${fileName}"\r\n`;
+    const safeFileName = fileName.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
+    preamble += `Content-Disposition: form-data; name="${fileFieldName || 'file'}"; filename="${safeFileName}"\r\n`;
     preamble += `Content-Type: application/octet-stream\r\n\r\n`;
 
     const epilogue = `\r\n--${boundary}--\r\n`;
@@ -216,6 +217,7 @@ class VidmolyUploader {
       yield preambleBuf;
       const fileStream = fs.createReadStream(filePath, { highWaterMark: CHUNK_SIZE });
       for await (const chunk of fileStream) {
+        if (signal && signal.aborted) throw new Error('Aborted');
         if (throttle) await throttle.consume(chunk.length, signal);
         bytesRead += chunk.length;
         yield chunk;
diff --git a/lib/voe-upload.js b/lib/voe-upload.js
index ec2479a..a76c2ca 100644
--- a/lib/voe-upload.js
+++ b/lib/voe-upload.js
@@ -228,7 +228,8 @@ class VoeUploader {
       preamble += `${sessionId}\r\n`;
     }
     preamble += `--${boundary}\r\n`;
-    preamble += `Content-Disposition: form-data; name="file"; filename="${fileName}"\r\n`;
+    const safeFileName = fileName.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
+    preamble += `Content-Disposition: form-data; name="file"; filename="${safeFileName}"\r\n`;
     preamble += `Content-Type: application/octet-stream\r\n\r\n`;
 
     const epilogue = `\r\n--${boundary}--\r\n`;
@@ -244,6 +245,7 @@ class VoeUploader {
       yield preambleBuf;
       const fileStream = fs.createReadStream(filePath, { highWaterMark: CHUNK_SIZE });
       for await (const chunk of fileStream) {
+        if (signal && signal.aborted) throw new Error('Aborted');
         if (throttle) await throttle.consume(chunk.length, signal);
         bytesRead += chunk.length;
         yield chunk;
diff --git a/main.js b/main.js
index 0611a01..55fe9b3 100644
--- a/main.js
+++ b/main.js
@@ -802,6 +802,10 @@ ipcMain.handle('import-backup', async (_event, password) => {
   if (canceled || !filePaths.length) return { ok: false, canceled: true };
   const buffer = fs.readFileSync(filePaths[0]);
   const imported = backupCrypto.decrypt(buffer, password);
+  // Validate imported data has required structure
+  if (!imported || typeof imported !== 'object' || !imported.hosters || !imported.hosterSettings || !imported.globalSettings) {
+    return { ok: false, error: 'Backup-Datei hat ungültige Struktur (hosters, hosterSettings oder globalSettings fehlt).' };
+  }
   // Safety net: timestamped backup so multiple imports don't overwrite each other
   const ts = new Date().toISOString().replace(/[:.]/g, '-');
   const preImportPath = configStore.filePath.replace('.json', `.pre-import-${ts}.json`);
diff --git a/renderer/app.js b/renderer/app.js
index 99a6e87..bdc1c5f 100644
--- a/renderer/app.js
+++ b/renderer/app.js
@@ -1310,7 +1310,9 @@ function getSelectedJobLinks() {
 
 // --- Upload ---
 async function startUpload() {
-  if (healthCheckRunning || uploading) return;
+  if (uploading) return;
+  // Wait for any running health check to finish (e.g. startup auto-check)
+  while (healthCheckRunning) await new Promise(r => setTimeout(r, 100));
   uploading = true; // set immediately to prevent double-click race
   updateQueueActionButtons();
 
@@ -1345,35 +1347,43 @@ async function startUpload() {
     }
   }
 
-  queueJobs.forEach(j => {
-    if (j.status === 'preview') j.status = 'queued';
-  });
-  updateQueueActionButtons();
-  renderQueueTable();
-  updateStatusBar();
+  try {
+    queueJobs.forEach(j => {
+      if (j.status === 'preview') j.status = 'queued';
+    });
+    updateQueueActionButtons();
+    renderQueueTable();
+    updateStatusBar();
 
-  const uploadPayload = {
-    hosters,
-    jobs: jobsToStart.map((job) => ({
-      id: job.id,
-      file: job.file,
-      fileName: job.fileName,
-      hoster: job.hoster
-    }))
-  };
-  const result = await window.api.startUpload(uploadPayload);
-  persistQueueStateSoon();
+    const uploadPayload = {
+      hosters,
+      jobs: jobsToStart.map((job) => ({
+        id: job.id,
+        file: job.file,
+        fileName: job.fileName,
+        hoster: job.hoster
+      }))
+    };
+    const result = await window.api.startUpload(uploadPayload);
+    persistQueueStateSoon();
 
-  if (result && result.error) {
-    alert(result.error);
+    if (result && result.error) {
+      alert(result.error);
+      uploading = false;
+      updateQueueActionButtons();
+      updateStatusBar();
+    }
+  } catch (err) {
     uploading = false;
     updateQueueActionButtons();
     updateStatusBar();
+    alert(`Upload-Start fehlgeschlagen: ${err.message}`);
   }
 }
 
 async function startSelectedUpload() {
-  if (healthCheckRunning || uploading) return;
+  if (uploading) return;
+  while (healthCheckRunning) await new Promise(r => setTimeout(r, 100));
   uploading = true; // set immediately to prevent double-click race
   updateQueueActionButtons();
 
@@ -1407,30 +1417,37 @@ async function startSelectedUpload() {
     }
   }
 
-  jobsToStart.forEach(j => {
-    if (j.status === 'preview') j.status = 'queued';
-  });
-  updateQueueActionButtons();
-  renderQueueTable();
-  updateStatusBar();
+  try {
+    jobsToStart.forEach(j => {
+      if (j.status === 'preview') j.status = 'queued';
+    });
+    updateQueueActionButtons();
+    renderQueueTable();
+    updateStatusBar();
 
-  const uploadPayload = {
-    hosters,
-    jobs: jobsToStart.map((job) => ({
+    const uploadPayload = {
+      hosters,
+      jobs: jobsToStart.map((job) => ({
       id: job.id,
       file: job.file,
       fileName: job.fileName,
       hoster: job.hoster
     }))
   };
-  const result = await window.api.startUpload(uploadPayload);
-  persistQueueStateSoon();
+    const result = await window.api.startUpload(uploadPayload);
+    persistQueueStateSoon();
 
-  if (result && result.error) {
-    alert(result.error);
+    if (result && result.error) {
+      alert(result.error);
+      uploading = false;
+      updateQueueActionButtons();
+      updateStatusBar();
+    }
+  } catch (err) {
     uploading = false;
     updateQueueActionButtons();
     updateStatusBar();
+    alert(`Upload-Start fehlgeschlagen: ${err.message}`);
   }
 }