So did it worked before? What was done before the issue caused?  Installed any Providers or modules ? 

Try to restart the application.  Try to clear Server Cache.  Try using a other browser.  Check permission and IIS Settings. Any other installs on the Server?

Source package is the source code of the DNN Platform for developing.  But it Looks as it isn't a develope instance.

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Regards

Matthias

DNN MVP

www.aarsys.de

Metro7 Skin

ShoutCastStats Module for DNN

The problem has reappeared. Before I had restarted the application from IIS and it worked fine. I have tried with different browsers (Firefox, Chrome, IE 10 and compatibility mode). What I have done a few weeks ago was to try and update the blog module. I have copied the application files and backed up the database. After I failed to update the blog, I have restored the database and the application files. I doubt this could have influenced the problem. 

Thank you for the help! I really hope we can fix it together somehow!

I've checked the permissions for the dbo user and it appears to be the db_owner. I suppose this gives it all the possible permissions that it might need. Besides that, I am able to add an user using the admin page "User Accounts". A little more than a month ago, the website was moved to a new server. It switched from IIS6 to IIS7 and maybe even the sql management studio is newer on the new server. Could this have affected the user registration in any way?