With the new undo/redo MovCaptioner is supposed to create a folder in your MovCaptioner folder called "Temp". It should create this folder on its own to hold scratch files as you work, then it will delete them all when you're done. If it does not create the folder, it may cause the problem. Make sure that your MovCaptioner folder is in your main hard drive's Applications folder, then simply create a folder called "Temp" in your MovCaptioner folder. That should solve the problem. Opening a previously saved project should also create this folder. I've added this folder to the new zip file so it should be there in the future to prevent this.