Uh... well, you're gunna just have to hunt for any entities set to rendermode glow.
Or, you could do this:
1. Open your map
2. In Hammer, File -> Export to .MAP
3. Locate the newly-created file and open it in Notepad or another plain-text editor (
not Word, Wordpad, etc).
4. Edit -> Find (or program equivilent), and search for:
"rendermode" "3"
Just like that, quotes and all. That will skip to the first entity set to 'glow'. If you find, on the line below, a curly bracket
{, then, on the next few lines, lots of co-ordinates, then you've found a brush-based entity. Remove the "rendermode" line and all will be fine and dandy (assuming you've only done it to that one brush).
If you're still stuck, e-mail me the RMF or upload it to the Map Vault