Network printer password problem

I work at a University. We have two network printers in the building. Both printers require a password to be entered in order to print. Here's the procedure: 1) Use File - Print or command-P 2) choose the printer and settings 3) press enter or click print 4) a window pops up asking for a password 5) enter the password.

Step 4 is where the problem occurs. Sometimes the window pops up. When it does, I am able to enter the password and the printer works fine. However, sometimes (quite often actually) the password pop up window does not pop up. When this happens it acts as though it's going to print. In fact, it sends the information to the printer, but the printer requires the password, so rather than printing my document, it simply prints and error page stating that I tried to print a document without entering the proper credentials.

I have searched and searched to try to find an answer to this problem. My University's IT department can't figure it out, and nobody seems to have posted anything on the well-known forums online.

Can you help? Can you tell me how to get my computer to forget that I've ever entered a password for the printer and ask me to enter it every time I try to print a job? That's really all that I need it to do.

PS - I am fairly sure that this isn't a keychain issue, as there doesn't seem to be anything saved for the network printers in the keychain utility.