I have pretty much moved all of my email domains and hosting over to Google Apps. It just makes sense – free email, spam filtering, etc. and you can access it via IMAP or POP.  It’s been working great too, but recently I started getting the following error from time to time in my Outlook client:

IMAP: Invalid credentials (Failure)

This was a new error and went away if I clicked on the remember password box and clicked OK, but it was annoying.  Luckily, after some research I found this fix: 

1. Close your email client
2. Go to https://www.google.com/a/YOURDOMAIN.COM/UnlockCaptcha and enter your username and password to unlock the captcha. (Obviously, replace YOURDOMAIN.COM with your own domain name.)
3. Restart your mail client.

The problem should now be fixed.