What's the "some error" that it gives? Details are important.
Open the project in Test Complete 11. It will ask if you want to update the project to be compatible with TC11. If you select yes then it will do the modifications to files. Note that the project will not be backwards compatible with TC10. I suspect Test Complete simply updates the version number in some xml files in the project suite (.pjs, .mds) and thats all. You'd probably want to keep a copy of the TC10 version in case you decide you dont want to run in TC11 for some reason.
