Try saving your map in a different directory (like the steamapps folder itself)
And try to compile it again... strange error I had a few times after the sdk update, this is the only fix I know so far :/
Possible problems, since you didn't say where it says this:
• You have a space in the name of your map, causing an invalid path that it "can't find"
• You have a fatal error meaning no BSP is being generated, so it can't find it. If this is the case you'll need to either tell us the real error near the beginning of the compile or past the log into www.interlopers.net/errors
Valve Software - vbsp.exe (May 7 2010)
2 threads
materialPath: c:\program files\steam\steamapps\ex3vious\team fortress 2\tf\materials
Loading C:\Documents and Settings\Ben\Desktop\pl_weapons_facility_b3a5.vmf
Entity 1955: func_areaportal can only be a single brush
Valve Radiosity Simulator
2 threads
[Reading texlights from 'lights.rad']
[34 texlights parsed from 'lights.rad']
Loading c:\documents and settings\ben\desktop\pl_weapons_facility_b3a5.bsp
Error opening c:\documents and settings\ben\desktop\pl_weapons_facility_b3a5.bsp
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