If you're running a version of windows Prior to WIndows 2000 it could very easily be Internet Explorer (versions less than 6 have this problem with the VB/PHP interpreters). You can upgrade to 6 or later (via Windows Update or you can do a goole search and look for the IE6 for IT Deployment )
If you're using FireFox/Mozilla, while they're awesome browsers, they are still in their toddler years so there are going to be some thing here and there that don't work quite right.
Hope this helps.
Oh yeah! If you're using any version of IE or Windows, try also updating it because that usually helps clear things like that.