Do you have a Form 2555 in your return? There was a unusual cluster of users getting that F1040-266-01 error on last Thursday night/early Friday. I reported it to TurboTax and never heard anything back, likely because that was the same day they moved everything to this new forum.
I'll see if I can give a Moderator a nudge today and will report back here if I hear something.
If you wish, you can phone TurboTax Support today.
Hours are 5AM-5PM Pacific (8AM-8PM Eastern) Monday-Friday.
FAQ: What is the TurboTax phone number?
https://ttlc.intuit.com/questions/1899263
