*** Tried to load non-VTF file as VTF file!

I encounter this error message in the console after I load the
map. I have not noticed any ill effect on the map itself, but
this sounds a bit ominous.

Here is the complete error message:

*** Tried to load a non-VTF file as a VTF file!

Error reading material "materials/maps/courthouse/c-462_288_-192.vtf"

Should I be concerned about this?

If you're noticing a pink and black checkerboard pattern on any faces in your map, or a texture is not appearing properly, this might be a problem. - The 'material' name seems to be coordinates - Look near there in the editor to ensure it's a normal texture (Like a regular 'concrete' texture, not the LightmappedGeneric dev texture, for example.)

Otherwise, it seems like it could be safely ignored.

Thanks, Rabid. All the textures in the map look fine, as far as I
can see. I took care not to use any textures for models or dev
textures, so I don't believe that's the issue.