That my friend is a RAM error.
I had it, only solution was to change RAMs, I suggest you borrow someone elses RAM before throwing them out tho (OR trying your RAMs in another computer and run HL2..)
Perhaps the warrenty is still active? In that case just change, that's what I did.
Edit:
Missed the post where you said that it only happened on your map.
I suggest you let someone else try the map and see if he/she get's the same problem.
But still, in either case it is RAM related.