Can you upload one of these files with the assembly an part files?
If you are on subscription, open a support ticket with your VAR.
Here is the drawing template file I'm using. I'm trying to load the attached sheet format and once I do I am unable to save. It is happening without any part/assembly files in the drawing.
I have raised a problem report with my VAR.
I had the same problem you have.
But the problem is with your Drawing Template and not the sheet format!
What I did was start a new drawing using the SolidWorks default template.
Then I replaced the sheet format with yours.
I could then do save-as template.
There is another thread about "crusty old templates" which I think applies to your situation.