Wow @rmkrtichyan thank you so much!! You jogged my memory and now I remember receiving said letter and being puzzled by it. While the TurboTax error description was very misleading, I'm also embarrassed that I could have avoided this whole issue.
For the previous years I was using 12 zeros for the CA SOS number as a general partnership.
The recent CA FTB letter assigned us a temporary number. The letter says:
"IDENTIFICATION NUMBER: TEMP #########"
where #s are actual numbers.
The Form 565 says SOS numbers are supposed to be 7 or 12 digits but I entered just the 9 digit number, filed last night, and the return has been accepted!
Thank you so much everyone who has been adding comments to this thread and trying to troubleshoot it together. @davidsakamoto @rmkrtichyan @Michelle7280 I wish you all weren't suffering like me but misery loves company...
