Autodesk support has
a page on this error in older versions of Inventor. I can't say if your problem is the same, but it sounds like there might be a program registry issue.
Do you have both 10
and 11 installed? If 11 was installed and you try to run 10, it will most likely need to re-register the paths for 10 in the Windows Registry. I believe that you have to have at least Power User privileges for it to do this, however. I run both versions and have regular User privileges at work and have to have an admin run the program each time I switch (gotta love Sarbanes-Oxley!).