Can anybody give me a tip what does this Vavoom error mean:

Init: adding ./basev/common/wad0.wad
Init: adding ./hexen.wad
Init: adding ./hexen.gwa
Init: adding ./basev/hexen/wad0.wad
Init: adding DRv2-1.WAD
- VWadFile::OpenSingleLump
- W_AddFile
- FL_Init
- Host_Init


ERROR: Segmentation Violation

I guess it's a problem finding or opening a lump, but it's strange it doesn't mention which lump has the problem <!-- s:? --><img src="{SMILIES_PATH}/icon_confused.gif" alt=":?" title="Confused" /><!-- s:? --> . EDIT: Now that I check it better FL_Init could mean flats initialization, maybe the problem is in a flat??

It's Lucas'es Dark Realms WAD. It ran well in original Hexen.

Ouch, this one discovered 2 bugs. The main problem is that in current version it does case-sensitive extension check. Rename it to be in lower case and it will be fine.

Should I make any modifications to my copy to prevent something like this from happening again?

That is the problem of Vavoom engine, not your wad, and I am sure this will be fixed in the next version; but just in case you may rename your DR wad so it has lowercase extension ("wad" instead of "WAD").