I've seen a few threads here and there about the hammer editor having issues and I've followed a few of them to fix it and came up unsuccessful. I'm hoping if anybody could give me a bit of help in getting the map to work. It works perfectly fine up until the loading screen with the little blue dots in the corner. After that point, the game just closes on itself.

Could anybody please help?

This is pretty annoying to fix since it could be any number of things. Either examine the things you changed between the last (working) compile and now, or if that isn't possible try hiding bits of the map using visgroups or cordons (see if your map compiles with all entities hidden, one room at a time, etc) to see if you can determine what is causing the crash.

Three main reasons the game might be crashing: You're using unfinished/buggy entities. If there isnkt much documentation about something, or it' sever used in the game Valve probably hasn't done much big testing on it and it may break if used badly. Another potential crash (less common) is entering wierd settings into entities. VBSP will crash for example if you use the wrong order of : an ; in instance input/outputs. The third is running out of memory due to excessive entity spawning. Check any cubedroppers or similar things to make sure they won't keep endlessly spawning cubes. (Doesn't really apply to other people's instances since they're probably bugtested enough to catch this sort of issue, but make sure it doesn't happen if you make your own.)

Wow thanks for such a fast reply. Unfortunately, this error has been going on since my first compile of the map, so I have no safe file to revert back to. I've pretty much imported the map straight from PeTI into hammer, and the only new entities added are a few linked_portal_doors.