Your card may have expired, the item you are trying to renew may not be a renewable item (e.g Interlibrary loan), the item may already have been renewed the maximum number of times, or another customer may have placed a hold on the title.
One reason that you may get a - Consult Library Staff - response when you attempt to renew, is because your record has been stopped due to a notification to you that has been returned as undeliverable. Please verify contact information on your account and make sure that your email server will accept messages from PGCMLS.