The first question you should ask is "what as changed since?".
Any recent Windows update?
Any change in the data? Especially where you look for your password?

Then again, it could be a corruption of the Workflow configuration file or of the Workflow Configuration program itself.

Have you try to run a repair on Workflow through the Add/Remove program of Windows?

You could also try, as a test, to set a static password in a local variable or a jobinfo and use that in DigitalAction. This way we can check if the problem is with static value in the password field VS a dynamic one, or if it is related to your data selection.