I was not amused this afternoon when my attempt to push to GitHub for the first time from a new (well, old) machine was met with the message

Failed to erase credential: Element not found

fatal: Authentication failed


A quick Google revealed that other Vista 32-bit users have had a similar experience. The solution (as described by gregfiske) was not to input my credentials into the Windows pop-up box, but to cancel it and input them at the subsequent command line prompts instead.