Just learned an important lesson that might save others a lot of time.

Do not put html in your product names or variant groups, etc. When it is sent to PayPal (maybe other gateways), it screws things up and the user just gets sent to the paypal front page: https://www.paypal.com/cgi-bin/webscr

In my case I had a break: <br /> in a long variant name to make things looks nicer, and it took a long time to work out why customers weren't able to pay.

Have you tried encoding the product name on paypal?

You really have two options

Remove the characters from your product names.

or

Log into your PayPal account at https://www.paypal.com
Click the Profile link
Click the Language Encoding link under the Selling Preferences column
Click the More Options button
Choose ISO-8859-1 from the Encoding drop down menu
Select Yes for ‘Do you want to use the same encoding for data sent from PayPal to you (e.g., IPN, downloadable logs, emails)?’
Click Save

Please let us know if this works or not.