I also received this error. I was able to get my Federal return to transmit after making a couple of changes - I'm not sure which one was the impediment, so I'll list all of what I did and maybe that will help.
1. freed up more processing power by closing a bunch of browser windows & tabs, and also closing out Adobe Acrobat.
2. after reading other suggestions about issues with form 8453-CORP, I noticed the pdf file I'd uploaded was huge (like 15MB) and I noticed that TT would convert an image, so I reduced the size of the image file of the signed form, and then uploaded that and made TT convert it to a PDF.
After doing that - I still noticed that even tho the software claims I could view the form by clicking "Attachments" in the upper right, there is no "Attachments" tab, button, link whatever, anywhere in the TT Business window. It was like this before too.
Anyhow, after doing all that, I clicked through and clicked Transmit thinking it would fail, but it worked.
Alas, because I had no way to view the attachment (and thus confirm the form 8453-CORP was included) prior to submission I did notice upon downloading the version of the return that was filed appears to have included the unsigned version of form 8453-CORP.
However, the thing is filed, and so I await rejection or acceptance. I'll keep you posted!
Now if only Oregon would accept efile from TT - off to print 26 pages to send by mail.
I hope that sharing this may help others with their tax compliance, which sadly gets more awful every year.
Best of luck to us all.
