I am also getting the same error message for a reservation that shows "This reservation was ticketed and confirmed on Sun., Jan. 19, 2014 at 6:08 a.m. Central Time:

We were unable to process your eTicket receipt. Processing may take up to 15 minutes.
If you continue to have problems obtaining a receipt, please contact 1-800-UNITED-1 (1-800-864-8331) or send an e-mail to [email protected] for assistance.
If you would like to request a new receipt and you completed your travel within the past 7 days, please click here and follow the instructions provided.
Thank you for choosing United Airlines

I can email myself a copy of the reservation from the "E-mail summary" link and it arrives, but I have not gotten a copy of the e-ticket receipt when I submitted the request through the "Add E-mail Address and Request Receipt" link.

Like everyone else, I just want to see the actual ticket numbers and ensure that my reservation is in fact ticketed.