The AOL browser as well as MSN Explorer are hacked up versions of Internet Explorer. They are both junk. The only purpose they serve is to take up valuable hard drive space on the computer unfortunate enough to have them forced on it.
For most people using AOL, their crappy browser works just fine, since they never really get to see what's out there on the rest of the internet anyway. They generally spend their days "keywording" and doing other "AOL" things that have nothing to do with the real internet.
Unfortunately, some AOL end users eventually end up on the real internet and then they start to see all kinds of problems like the ones your users are seeing (this may or may not be their problem, but I'd be willing to bet it is for most of them, the rest might be the victims of the latest "Windows Autoupdate", which is usually anything but a real update).
The reason for the red X problem is "security". There are so many things taken out of these hacked up versions of Internet Explorer in the name of "security", it's amazing these people can even see your page at all. Images that do not come from what they consider "trusted sources" are considered virus attacks and are blocked automatically. There is a similar problem with IE 7 and Windows Vista, but that's a whole other story, and one reason why I still run IE 6 on Windows 2000, without any problems (some of these issues cropped up with Windows XP and it's "personal firewall", but we won't go there either....)
I'll be quick here, but the main complaint people have about Internet Explorer is the threat of viruses, hijacking, etc.... It takes about 30 seconds to completely remove those threats from IE, but no one knows how to do it, so they blame Microsoft for all of their computer problems. I have been running IE almost exclusively for almost 10 years and the last virus I got was right before I stopped using any antivirus software at all.

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