Error in Doom Builder

Whenever I try to open "Edit MAINCFG..." in Doom Builer, I get this error.
I just want to know, is this error usual? Are there other files I need to install? I just want to make sure this can be fixed, so I don't have to use SlumpED everytime I want to edit my level's MAINCFG.

That error is indeed typical for someone who didn't download cmcs21.ocx separately and insert it in the same folder as SRB2 Doom Builder.

Just Google "cmcs21.ocx" and you should find it easily.

Or just listen to this post that makes it oh-so-easy.

http://mb.srb2.org/showpost.php?p=550526&postcount=635