I had similar issue a few days ago. I believe that when you back up 3rd party apps you must delete the file where you kept your previous backup. I had backed up my apps when v4 came out. I tried to backup for v5 and it wouldn't work until I deleted the file that I had saved for v4. It creates a folder and an .alx file...the .alx file being the same file name as the previous backup...I think...creates an issue. Anyway, once I deleted my previous backup, it worked fine.