I found what the problem is (at least for me). On the 7th of April I netfiled my taxes just fine. When I attempted to do the same for my wife I got the "famous" error. So today I tried to see what exactly is going on with the forms and found out the problem (at least what is applicable to me and my wife, but I am sure this might help lots of you guys too).
The software made a wrong decision that my wife's T936 is empty and it closed it. The form is NOT empty and I can see it.
So to prove the concept I printed to pdf twice - once selecting to "close unused forms" and once NOT closing unused forms. And voila - T936 was there, but ONLY if I kept unused forms open.
When netfiling you are not presented with this choice - to close or not and that's why you cannot netfile.
I just got off the phone with support trying to see how I can force to keep the forms open when netfiling but unfortunately there is no way.
Bottom line - you can print your forms, select not to close unused forms and snail mail it to CRA. This way if TT fails to deliver a fix, we will not be fined (at least those of us that owe money) for late filing.
Just my 2 cents.
