I've just started to build a tobruk pit so I simply made a hollow square in which i placed a sun, info_player_start and some brushes. The settings are HL2 default. Every time I try F9 I get this error:

http://users.pandora.be/conspectus/error.jpg

Check your hammer properties to see if the build programs are properly set up.

http://users.pandora.be/conspectus/build.jpg

Actually that's not much of a problem. The map was compiled but Hammer isn't able to start HL2. Try to start HL2 manually and load your map via console. With a little luck Hammer will stop complaining after that procedure. Refreshing your SDK content may help too (See SDK Menu).