We cannot process this transaction because there is a problem with the PayPal email address supplied by the seller. Please contact the seller to resolve the problem. If this payment is for an eBay listing, you can contact the seller via the "Ask Seller a Question" link on the listing page. When you have the correct email address, payment can be made at www.paypal.com.
There are multiple reasons for that error message to be generated, including (but not necessarily limited to!) the following:
1. There is a problem with the code of the button - typically with the BUSINESS variable being set incorrectly. The BUSINESS variable should show your PRIMARY PayPal Email address, NOT your Customer Service Email address.
2. Make sure you are making the purchase using the BUYER email address that you set up in your Paypal account.
3. If your product is a subscription, you MUST have a business or premier account. If you don't, this message will be generated.
4. If you're trying to do a test order with a zero dollar amount, it could generate that error. Make sure that you are testing your form with a purchase of something that costs at least $0.01.
5. If you have the "Content - Email Cloaking" plugin enabled on your site to help stop the spammers, the code for your business Email address might be being hidden. If it is, it will generate a message in the source that says:
To fix that, go to Extensions > Plugin Manager > Content - Email Cloaking and disable the plugin.
Hopefully one or more of these will help you to solve your issue!
The PayPal Developer Network is also a good place to look. They have a list of all of their error messages and possible corrective actions.