The latest version of Zen's Usage Checker in Firefox 3.6.16 works fine for me until I open another Firefox window either on the same machine or on another machine. Then it complains that the username or password is incorrect, which it clearly isn't. I get the same effect on Windows 7, XP or Ubuntu. Closing the first window doesn't help, in fact that makes it worse as it then stops working there when it's reopened!
Does the usage checker object to being accessed too often?
Grateful for any help with this though it's just a nuisance rather than important.