HI.

When i try to use sql express within a plesk configuration i always recive error

CREATE DATABASE permission denied in database 'master'.
An attempt to attach an auto-named database for file D:\inetpub\vhosts\arcticforum.se\httpdocs\App_Data\De.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.

it doesnt matter if the database exists or not.

Or ...

Failed to generate a user instance of SQL Server due to failure in retrieving the user's local application data path. Please make sure the user has a local user profile on the computer. The connection will be closed.

What user, how shall i do this i have access to the server but dont know how to fix this??

If you are using plesk or another managed system configuration, you must update the web.config file of your DNN installation to include the proper server, database, database user, and database password to connect to the database you created in Plesk rather than using the dynamically attached database.