Confused by "Authorize Computer" Form.

I'm trying to authorize my computer to use with a particular vendor.  I've chosen the Vendor (NYPL).  I've typed in my Vendor user name and password -- I assume those terms refer to the user ID and password that I use to access the Vendor.  It's rejected over and over, saying ID or password aren't correct (They are correct).  Am I assuming correctly?

Also, if I opt now not to authorize the computer, can I change that later?

Thanks!