"there was an error renaming/moving the output file
I believe this is triggered by inappropriate Merge Settings. Open Settings (the Gear icon), then click the "Merge" button.
Make sure nothing is set to PREFER_TIVO or TIVO_ONLY. You can also suppress
some such messages by selecting "None" at the bottom of that window.
The merge process involves selecting metatata from either a pre-existing pyTiVo style text metadata file (found next to the input video file and named video_name.ext.txt) or the metadata found by searching theTVDB or TMDb. It's complaining because the pyTiVo .txt file isn't there. I believe the program as distributed defaults to NOT looking for these files, so I'm guessing you changed merge settings at some point.
Note that if you click the "Outputs" button on the Settings Tab, you can select to never generate Text Metadata Files, which is what you should do if you do not use the pyTiVo style .txt files.