How can I get my DVD to eject on Pioneer DVR-RT500?

While dubbing a VCR tape to a DVD on the Pioneer DVR-RT500 recorder, this error message came up: "Disc Checking - Please wait about 15 minutes" - the manual only says that if you get this error message - "the power was abruptly turned off before writing to the disc was completed" - the power was not abruptly (or slowly) turned off - was dubbing for a 3-hour program and there was no power surge, etc. as I was in the next room and had a timer on to stop the tape - and then found the above error message and now unable to eject the DVD and the error message just stays on the screen - unplugged the recorder and plugged it in again and waited 5 minutes, and repeated this procedure many times, but this did not solve the problem. Any solutions to this problem?