Are you getting a message saying that there is an assertion failure in line 1763? If so, that's a known bug that is present in the game cds made for (in?) the UK; it's something to do with the manufacturing.
To fix it, you need a particular patch. Go
here, to download and install the patch.
When returning to a save game after installing a patch, it's important to make sure that the game uses the updated (e.g. patched) version of the map you are on. Otherwise, your saved game will also have saved the original error. I would suggest returning to an earlier save game. If you don't have one, maybe leave the map, save it there, clear your cache folder, and re-enter the problem area.