site access not allowed

I work for a national Drug Store chain, and I need to access our web
site from home. I can access the site, but when I try to log in I now
get this access denied message: > Due to the presence of characters
known to be used in Cross Site Scripting attacks, access is forbidden.
This web site does not allow Urls which might include embedded HTML tags.

I've always been able to log on with my old computer running on XP Home,
but since I purchased a new laptop last month running Vista Home, I
can't log in. I've done a few Google searchers and have found a walk a
round from IBM that I don't understand, nor am I sure I should attempt
to download and install them on my Toshiba Satellite.

Any help would be greatly appreciated as I'm completely stumped.

Thanks,

Joel