I've seen this myself with a few various games throughout the years, and I never did find a definite solution. The problem is, it could probably be related to a number of reasons: poor development design, script errors, compatability, incorrect dll, the list could go on.
Here's a few links to other forums that discusses similar issues (primarily with RGSS instead of RGSS2). You may be able to test some of these out with RGSS2 and see if it helps resolve your issues, but it's one of those things with random fixes that work for some but not all, so all we can really say is to try them out and hope for the best.
http://rmrk.net/index.php?topic=34817.0http://rpgmaker.net/forums/topics/10453/http://www.rpgmakervx.net/index.php?showtopic=34705