Not a big deal. You probably made your own texture map. What size did you save it as? Try resizing it to one of these numbers 32, 64, 128, 512, 256, 1024. They size does not need to be square.
Full Error:
CTextureFrame::GenerateMips_HemiOctAnisoRoughness(970): Cannot filter non-power-of-two texture 600x600x1!
CResourceCompilerTexture::CompileResourceInternal(692):
Error calling GenerateMips( “HemiOctIsoRoughness_RG_B”, nFrame = 0 )
for file “z:/steam/steamapps/common/sbox/core/materials/architecture/my_texturemaps/station_small_map_bottom_wall_normal_jpg_d1cea1c0.generated.vtex”!
[FAIL]
ProcessTexture(811): Error calling CompileImmediately(
Z:Steamsteamappscommonsboxcorematerialsarchitecturemy_texturemapsstation_small_map_bottom_wall_normal_jpg_d1cea1c0.generated.vtex ) for Z:/Steam/steamapps/common/sbox/core/materials/architecture/my_materials/basic_train_station_block.vmat!
CResourceCompilerMaterial::CompileResourceInternal(1756):
Error processing texture g_tNormal
