anyone ever had this error?

[o0OpsyphiO0o]

I was painting the alpha's on some displacements with custom materials I'd thrown together out of Ep2 textures for testing purposes. Then out of nowhere a hammer freezes, after about 30 secs my screen becomes weird random pixels start popping up like my display had gone all snowy but staggered, a popoup opens telling me that it succesfully converted the .wad to a .vmt and then let's me go on... but the crazy snowy thing remains... I reset the computer and I'm back.
Anyone ever seen this?