I've installed Autodesk Inventor 2011 on Windows 7, licensed under the TechShop promotional program. Install went OK, and the program will work in "Try" mode. But activation with the Techshop-issued keys fails with a 901 error.
I can't find any reference to a 901error in the documentation, support forums, or even in the FlexNet End User Manual. (You're using FlexLM/ FlexNet? That was a turkey 10 years ago, and acquisition by Macrovision didn't help.)
The appropriate "alternate way to activate" email has been sent (ref "AutoCAD Inventor Professional Suite 2011 358-XXXXXXX", from "firstname.lastname@example.org") has been sent, but no reply has been received.
I am not very sure about what's the actual reason, but you may also want to contact the Autodesk Business Center team here besides waiting for the feedback from Activation team which you have sent email: