From the Helpdesk:
We’ve seen several Mac loaner laptops over the past few weeks that wouldn’t let people in. Re-binding them to the domain usually fixes this. Nate recently added Mac loaners with Casper (which ought to be all of them, but may not be) to a group that will automatically re-bind them to the domain once on startup.
So, if you can’t get into a Mac loaner, please make sure it’s plugged into the network, restart, wait 2 minutes for Casper to do its thing, and try again. This may save you a trip to the helpdesk. If that doesn’t work, of course, let us know as usual and we’ll take care of it.