Yeah this was paypal response to me.
Thank you for contacting PayPal’s Merchant Technical Services.
When setting the enctype="multipart/form-data in the form tag of a button, and you are specifically passing across prepopulation variables with null values, an Internal Server Error is given. This is a known issue that our developers are working to resolve. At this time, I unfortunately, do not have a timeframe as to when this issue will be resolved. You will be notified as soon as it is. I apologize for the inconvenience.
Workaround - If you would either remove the null variable from being passed over, or remove the enctype this should resolve the error.
Merchant Technical Services
PayPal, an eBay Company
But to resolve the issue i have put some standard buttoms and limit to 1 product out of 3 but my clients are very upset about the whole situation im also desperate but as you can see here no one care or can't help us out without say that with some coding will fix it lol. But im not a coder my self so im stock with no solution. Lets hope a very smart person willing to help can help us out wiht some instructions to change the code of the shipping that is my guess to where can be some null values. Hey even i can send some donations to this smart peopel but who knows if i find a solutions i will post it here for sure.
Lets hope for a solution soon either paypal or some one else.
Santos