Just an educated guess, but you've probably reached some threshold where 2GB of RAM isn't enough any more. In my experience, 2GB can by marginal depending on what else is loaded and running in the background.
As mentioned above, this has been going on for years and nobody really knows what the cause is. Personally, I suspect that it tends to happen when memory is tight and there is a lot of swapping out to the virtual memory pagefile.
If it were my system, I would add RAM if practical. If that's not an option, I'd do everything possible to free up available RAM. I've gone as far as to make a separate login account on my laptop for gaming. That account loads a bare minimum of startup items, runs a minimalist desktop, etc. If nothing else, I get a few more FPS on that profile because the client doesn't have to do quite so much memory swaping.