I tried to use a light instance but it won't show up in my camera view and when I try to compile the map with the instance in it still I get this message:

ConVarRef gpu_level doesn't point to an existing ConVar
Could not open instance file instances/lights/bts_light_fluorescent _01_128b.vmf

What the hell?!

Is your map saved in the "portal 2/sdk_content/maps" folder? Saving your map anywhere other than that folder can sometimes cause this to happen.

Oh, well I just checked and it's in the HammerAutoSave folder.