Getting unknown error during opening file in inventor 2011, while i have installed 2010 and 2011 both on same systems.
When in doubt, try a different file. You may have to recover a older version from the "Old Versions" folder.
I've experienced the same error when I wanted to open a file saved in 2013 with Inventor 2011. Normally Inventor should come up with some kind of message that the database has a newer scheme. However I got to see the RSE stream error.
Could it be possible that this file is saved in a newer Inventor version? Maybe you've got it from a third party?
Best regards, Daniël
It sounds like it has been come damaged, either restore from a back-up or from the "OldVersions" folder within your work directory.