[Fontaine]

Had a similar situation. Glowing squares -- white borders, gray inner area. Usually on terrain/ground brushes, both single player and multi-player. Then had the effect of SH crashing everytime I started a server, dedicated or not, regardless of the map or map rotation I used. I removed all but a few of my add-on mods (maps, skins, effects) and the problem was resolved. SH appears to have a lower limit for add-ons than MOHAA does, perhaps because it is an add-on, but I may (and possible am) wrong on this.

Anyway, try moving you mods out of your main folder temporarily, and see if that doesn't help.