Have a look at one of these articles:
http://www.dynamicscrmpros.com/scribe-fails-connect-microsoft-dynamics-c...
http://www.dynamicscrmpros.com/solve-error-id3242-security-token-not-aut...
If for some reason your CRM org was moved or upgraded you may have been sent to a new crm url. Open Settings -> Customizations -> Developer Resources and see if the url has changed. I had one a few weeks back that went from https://disco.crm.dynamics.com to https://disco.crm9.dynamics.com
changing that setting in scribe fixed my issue.
I hope one of those solutions helps!
-Josh
