Jim, we'll assume that you have a Time Capsule, correct? If yes, power off the Time Capsule, wait a few minutes, then power it back up again. Restart your Mac as well.
Then hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the screen
Select Verify Backups
The process might take anywhere from 10-60 minutes depending on how much data is stored in the backup on the Time Capsule. Let the process run until it completes or until you see an error message. If a message appears, post back with the exact text of the message.
Once the process has started, you can check on the progress of the operation by holding down the option key and then clicking on the Time Machine "clock" icon.