[Plugin: NextGEN Gallery] does not rescan folders or upload images

Any error message, at which point does ir stops / freeze ?

No there was no error messages. The thing would freze instantly when doing a scan of a folder and within a few seconds when trying to upload images or zip file.
I have not tried again since then as I have had some weird issues with my hosting.

I have tried it today again with a fresh installation of the WP and it was the same thing. I could not upload a zip file and it would not scan the folders

Strange, no error message are very unusal… have a look to the server log files (if you have access) maybe there is something noted

Good idea. Thanks a bunch.

I am also wondering whether I am uploading the plug-in wrong. I mean the transfer typ that I should be using when uploading it