search google for 'paypal bad request' and you'll find 100s if not 1000s of people with the error
"Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit."
If you are going to write excessively large cookies then at least have the decency to handle them. People should not have to clear their cache just to use PAYPAL.
People are losing sales over this.
This is unacceptable and highly likely easy to fix. You have been ignoring this for months if not longer.
