Are you running a firewall, protection proggy, pop-up stopper or antiviral system? I've found on occasion that any combination of these may create this situation. (They are busy here in the forum with WebTrendsLive, a site monitor.) While I'll admit IE gets plain wiggy, it makes no sense when your cache is near full, that the sytem would opt to start saving images in a larger file size format. Mozilla doesn't appear to have this problem and tech tv recommends Avante-browser (with built in pop-up blocker). You might want to switch.