In the last two days, received emails with an attached pdf will not open. Instead I get the following message "The current operation on "INBOX" did not succeed. The mail server for account 3RDS.COMLLC. Earl responded - nz number." I am running Thunderbird 3.1.7. I can login to my ISP email server and see the downloadable pdf's. The ISP has made not changes to their service and the pdf's are not large. Suggestions???