When Slotmonster asked me to try out the games, I kept getting "unsupported browser" issues. I had everything updated, and am running XP and IE 8. At the time, no cause for this could be found, and Slotmonster assured me the site should work fine with XP and IE 8.
More recently, and down to a completely different issue unrelated to casinos, I might have found the problem. It's pretty obscure, and is documented as a "corrupt user agent string" by Microsoft. It is caused by badly coded browser plug-ins, and other installed software that adds it's abilities to this string.
The user agent string is sent to websites in order to inform them of the abilities the viewer can support. Unfortunately, there are two types of corruption. One is that the string exceeds 256 characters, but is not actually corrupt, and the other is that plug-ins have misused it by adding a duplicate or invalid entry.
Fixing the problem involves editing the registry, but Microsoft have provided a "fix tool" that will rewrite the registry entries and remove the corruption. There is also a diagnostic tool to determine whether the problem exists. Having applied this fix, BigCasino no longer produces this "unsupported browser" error message.
This appears to be the solution to the problem.
The suggestion is that since this is a common problem, the website should be updated with a tool that can read user agent strings that are longer than 256 characters, and can tell when it is merely duplicate entries that make the browser appear to be something other than it is. Microsoft have addressed this issue with Windows 7 and IE9 by limiting what third party software can do with the user agent string. With IE9, although the software will still write it's own entries to the registry, IE9 will NOT send them in the user agent string, thus only a "clean" user agent string will be seen by the website, regardless of how "dirty" the coding is in any software or browser plug-ins.
Reinstalling IE alone does NOT solve this problem, the registry has to be cleaned up too. Even Advanced System Care fails to spot a bad user agent string configuration in it's registry check, hence I never managed to fix the problem by running this and other tools.
Although fixed now, I expect the problem will reoccur in the future, as other "dirty" coding afflicts these entries.