This seams like an encoding issue on PayPal's end. I've no idea what encoding they're sending data in, but doesn't seam to be UTF-8. Navigate to the below URL after logging into PayPal.
www.paypal.com/cgi-bin/customerprofileweb?cmd=_profile-language-encoding
Next click More Options then change "Encoding" to UTF-8. I don't know why they hide this like crazy, but that sometimes can be the cause as Joomla, CB, and CBSubs all exclusively use UTF-8. Once done retry a test payment and see if that works. If using a sandbox account you'll need to change the domain in the link above to their sandbox domain to reach that page for a sandbox account.