(1) I didnt see you specify a texture or other effect (like the embedded { }'s in xandaxs's post) (2) you probably have some other brush underneath/inside your water brush that isn't nonsolid
if your own map doesn't show up, a common problem is that you're still seeing an older version of the generated minimap -- if you delete it, it will regenerate a fresh one
Being admin is not the same as having write privledges... see if you can make a new text file or something in your q3ut4\maps folder WITHOUT clicking through any UAC prompts
It's fairly common for net images to use progressive, so you will often at the very least have to re-encode them. I'd also check their size to try to normalize it to something convenient for q3 offset/scaling. Try move ALL of your textures out of your texture folder and see if it still crashes. If o...