Add more info about your system, as detailed in https://retropie.org.uk/forum/topic/3/read-this-first.

Installation logs are kept in $HOME/RetroPie-Setup/logs - get the latest log from there (you'll need SSH to copy it), then post its contents on pastebin.com.

The error is a generic one, the root cause for this should be detailed in the log file.

@sdabbs
I don't know sorry. Try using pip to check and upgrade py modules.

pip list pip upgrade xxx.xxx

I had a go at making a list of all the 'optional packages' and which emulator does what. I realise this will update and change regularly, but I hope this still helps someone out there!

https://timleesongs.wordpress.com/2018/08/22/retro-pie-optional-packages-full-rundown/