Changing IP Addresss

"Your IP address does not match the one last used to access the thank you page Please use your Back button to go back to the thank you page then try refreshing the page in your browser. Please contact customer support if you continue to have problems".
******************************************
I get the above message in response to Pay Pal activity where a book download was paid for. When I receive the sellers acknowledgment with the download link, I receive the message [above]. I've tried acting upon the error message with no success. I've not had this problem before.
Who is "customer Support" referenced in the message?
Any ideas? Thank you.

 

Thank you for the prompt replay. I'll do that.