Oh, yeah, that’s probably it. The 1.5 code is like, 4 months old by now.
I don’t remember CSGO crashing on material import here, but it’s been months since I did it. Which subfolder is it?
The thumbnail option is new in 1.6 as well. You might want to update to the latest version, “HammUEr 1.6 preview for 4.12 (D3 ASE & LWO)”.
Ignore the “preview (D3 ASE&LWO)” bit of the name, that’s mostly for the Doom3 & Quake3 stuff that still needs testing.