Have a scheduled workflow that pulls any active customer record, looks the value of a custom field driven by a saved search (with store value unchecked) and then populates a hidden field with the value, so it can be used on a saved search. However, I am receiving two errors: "please enter a valid email address" and "record has changed"--the email field is not being touched by this workflow nor is email required on customer records. Any idea why these keep cropping up? It appears to be working otherwise.

Have a look at the field sendtransactionsvia. The record could have "send transactions via email" checked. No clue otherwise, I'm afraid

Thank you. It is not checked, unfortunately.

Has the customer got "allow login" enabled? That's the only other situation I can think of where an email address is required

@J-Mack could there be another script or workflow running in the background? Something is updating and submitting the record before you actually submit it in the user interface. I would love to take a look at it if you think that would be helpful.