Quote from Jepp on May 11, 2012, 7:25 pm

I had the problem with the vvis aswell but lp's fix worked for me!

lpfreaky90 wrote:

Quote from a valve employee if you're still experiencing problems with hammer:

Quote:

You'll need to delete vbsp.exe, vrad_dll.dll, vrad.exe, vvis_dll.dll, and vvis.exe from your bin directory, then re-verify your Portal 2 cache.

The issue is that the build tools in SDK were colliding with the tools now packaged into Portal 2. By deleting the files, Portal 2 should put the correct files back on your disk.