when start Autodesk Inventor 2012 i have this problem.
An autodesk product failed to send the required value for SerialNum
an Inventor crashed
I would contact your VAR. See what's goiong on with your subscription license.
I solved it this way:
Try deleting this folder (with Inventor closed):
c:\users\<your user name>\AppData\Roaming\Autodesk\Inventor 2012
This folder will be regenerated the next time you start the application
Hope it helps!