Hello Laszlo,
com/microfocus/eclipse/project/content/FileTypeHelper refers to one of the classes in the plugins we ship with the product. If I had to speculate, it is complaining it does not know how to handle one of the extension types in the imported project. Perhaps you have some custom extension types in the project defined and those definitions did not migrate to 2.2.
We will need a test case of what you are trying to import from 2.1.
Recommend you file a support ticket as you will most likely need to submit a test case for further study.