Hammer Editor Crashing

Hi there,
Every time I open my map file (pretty big map file) hammer crashes on me while reading chunks.
I have a Intel core 2 CPU, 6600 @2.40GHz 2.39GHz
4.00GBs of ram, 64 bit system. Windows rating of 5.8.
It only happens with one specific map called sdk_Metal.
I opened the map, then while it was opening I went to Firefox, then I was about to go back to the map and hammer editor wasn’t opening.
This happens every time, and its a very important map file, i have worked on it for like 3 months now.

Also, a error just came up saying…
" Run time Error!

-pure vital function call.

Post compile log in [noparse]

[/noparse] tags.