Hello Dave,
Has your email template changed? When you are in your estimates screen, click More actions... and choose Customize Print Templates... . In the popup you will see a list of transactions with their associated print template. For estimate, has it been changed to another report? The default print template for estimates is Estimate (Custom). If a dropdown is blank, then the default print template is being used.
I would not associate the inability to log in with the estimate report. If you are having trouble logging in, give us a call on the Method support line 1-888-925-238 x2. We can help you out and take a look and any problems you may be experiencing.
Greg