Hi Tobias.Nink
May I ask what version of the game you are currently running? (You can see your version in the lower lefthand corner of the main game menu)
I have seen people with crane problems before who had earlier versions and patching the game to the latest version fixed it for some of them, so maybe you need to upgrade?!
If you run a version lower than 1.4.2, you might want to download and install the 1.4.2. patch.
Depending on the version that you now have, you can - if needed - get the appropriate file here:
http://www.shipsim.com/downloads/patches.php
Regards,
Fred