I built a co-op chamber in the PTI. When I clicked "build and play puzzle," the progress bars went through as usual until the very end. The "calculating lighting" progress bar was almost done when the game crashed to the desktop. I tried again and the same thing happened. I've tried verifying the game cache several times. Nothing helps. Any ideas? I really want to try out my map! (no point in building it if you can't play it)

Bump. I'm having the exact same problem, and I'd like to find a solution!

I don't really know what's happening but here's somethings you can try.

1) Create a new level; don't do anything in it but try to compile it.
This should work, if you crash here you have a problem with portal, not your map.

If the empty level also crashes, try to verify your game cache.
If that doesn't work, go to portal2/bin/ and delete vrad.exe vvis.exe vbsp.exe vrad_dll.dll and verify the game again.
If that doesn't work delete portal2/portal2_dlc2 and verify again.

If your test level doesn't crash then the problem is in your map! Try to remove some lights and see if that eventually fixes it!

Try removing some of the entitys.
Also does a error message some up after closing?

This is in a brand new map. Crashes to desktop. Very annoying!

EDIT: Actually, I just fixed it. Apparently it had something to do with the Sixense Motion Pack, as adding "-nosixense" to the launch parameters fixed it. Just right-click Portal 2 in Steam, click "Set Launch Options", and add "-nosixense" to the end of the text box, without quotes, putting a space before it if necessary. If the text box is blank, just fill it in with that.

If you don't have Sixense Motion Pack, this will almost definitely not fix it.