There's two ways to fix this, either:
Go to /raw/images/ and find any iwi file in there, copy it and then rename it to "~-gblockout_asphalt_test_c". Now you can compile it.
Open the level with the compile problem in it with radiant and change brushes with this texture:
(Image removed from quote.)
to any other texture you want to have in that place.
I found the image, and my browser saved it as a different name, so I had to rename it and now it works, thanks for the help anyways.