Migration Manager for Exchange has been installed, durign setup the initial request for license was skipped, then "Migration Manager for AD" component has been unselected from setup. License was applied and installation finished. Exchange data tab of the product is working, but in AD migration only the Open Project button is visible. Clicking it doesn't do anything, going to File | Open Project has no effect as well.
This is caused by Migration Manager for AD exclusion from setup and the AD license part not being applied.
In order to resolve the problem, go to Help | About, highlight Migration Manager for AD, click Update License and browse to the same MigrationManagerEX-*.asc license file that was used during setup. Every QMMEx license does have the AD part.