I was trying to import a Site Collection from one environment to another. I fired of the import command from a backup file created from stsadm -o export command. Then I created a new web application and a new  Blank Site Collection. I then ran the stsadm -o import command but received this error:

"FatalError: The specified user [username] could not be found"

There wasn't much on this, reading around I found that the person you are running the command line as must be the Site Collection administrator. I guess this makes sense, but would have been nice for the error just to say so!

Once I overcame this error I got a subsequent error:

"Error: Unable to read cabinet info from [filelocation]
FatalError: Failed to read package file."

SharePoint land didn't have any answers for this one either...but I did notice that some posts exported to a .bak file extension and others used .cmp. Using .cmp created multiple files and this worked fine.