Thanks everybody who supported me!
I found an old version of the hack at the kind friends of kindleblog (http://blogkindle.com/category/kindle-hacks/
), downloaded it, and applied the uninstall.
I then did a hardware-reset of the kindle.
After that I downloaded the update from the Amazon site directly to the Kindle.
And it worked. I have now Version 2.3 on my Kindle DX.
I attached the old hack file here just in case somebody else runs into the same issue.