Thanks for your replies...
Doh! I really was tired last night, sorry guys. Firebird works fine, its Mozilla 1.6 that I was, and still am, having problems with - I decided to give standard Mozilla a go for a couple of months, as I'm yet to settle on a browser I like.
Anyway, I've tried pasting the URL of an AOrg forum page into Mozilla - still the same error. Might try installing a different flavour of Mozilla today, then I won't have to browse the site using IE... Strange though, because in the week or so since I switched from Firebird, I've had no other problems and have been browsing and posting on the site fine...
I'm still intrigued by the error...is it telling me that the URL is too long? And if so, why don't I have the same error with other browsers?
Ok, it's maybe not that important, and I could just use a different browser, but I'm intrigued now as to what's causing it.
Cheers