The Login Data are saved on encrypt data in the Database.  To prevent brocken the Login data you have to use the same Maschine Key.

You did not descript what you have changed, what DNN Version you are using or if you using the origninal Usermanagement and Login. 

If you done a upgrade with the Upgrade package you should have used the correct Maschine Key, if you used a install package you have to modify the web.config file before upgrade with the same settings for the 2 SQL Server strings and for the objectQualifier and databaseOwner as you have used on the old version.  A backup of the old database and files, specially the old web.config file obligatory.

If you used a wrong Maschine Key DNN want install as a new instance and create new all database artifacts whish prevent you to use existing user registrations!

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Regards

Matthias

DNN MVP

www.aarsys.de

Metro7 Skin

ShoutCastStats Module for DNN