he mean when apply texture to shader, like diffuse, opacity, speculiarity mask.
well first check textures if something is wrong when you import, remember use DXT3 when you import into unrealed, anyway is strange normally if something is wrong just UnrealEd freeze, in your case particular is rare, anyway if still getting problems unistall and install fresh install of unrealed and try make a new file just with a texture exported with umodel from original client, in that case still getting error try open the tga o dds texture and save again in tga or dds but won't overwrite orignal, gl.