Doom Builder should install this...

On another pc(not mine), Srb2 Doom Builder won't install everything. One of the files that weren't being installed were cmcs.dll, which is apperently needed for level headers to be edited AT ALL. There's another file not being installed, but so far, I haven't proved it important.

Same thing happened to me, but all I did was download the needed files and register them with my system or moved them into the directory of SRB2 DB and now it works perfectly.

I don't think that SRB2 Doom Builder was suppose to supply the files.

Why do you even want to edit level headers with SRB2DB? Aren't the options in it a tad outdated? Try a lump editor.

http://wiki.srb2.org/wiki/Level_Header