I think it would be really cool if we could also use "Slight" GUI enhancements with this mod. The two don't appear to be vastly incompatible, but maybe I am wrong.

The error message that pops up is also very confusing. So if some form of compatibility doesn't work, make sure whoever tries too gets a less confusing error message.

I can’t really do something against the confusing content of error messages lmao. Java is generating these and they are very helpful if you know what to do with them :D
And if the error message is some of my custom warning/error outputs, these are more for me to better understand what’s happening when users report errors with logs.

This mod is on FancyMenu's incompatibility list and adding support for it is not planned, I'm sorry..

But thank you very much for your report!