I was compiling a map in hammer when:
LoadPortals: couldn't read c:\programfiles (x86)\steam\steamapps\common\portal2\sdk_content\maps\test.prt

WHAT IN THE WORLD IS A .PRT?
If anyone could help me with this problem, I would be happy.

prt is portalfile. if you don't have the portal file that means that vbsp couldn't make a nice portalmap.

THAT means you have a leak!
Time to fix some leaks