Well, while trying to get my crazy r2d2 unit ingame, I got this error message that I don't understand

Message Severity: 3
.\Source\Entity.cpp(218)
Entity base class "com_hero_default" not found

Help?

Did you copy the common folder into your sides folder? That contains the file you are missing.
If it is: search the folder for that file. If it isn't there, post back.
If it it isn't:
The common folder you need is in assets/sides.

like data_abc/common into the sides folder? why can't I just copy the com_hero_default into my sides folder?

The common folder contains a lot of vital files for sides to work. Chances are, you need it and it's good to have it there if you're using custom sides.

kk I just moved it into my sides odf file and it worked, thanks