Hi piccmi,
I had this error sometime ago when I use to use shared hosting on DNN 4 but one of my clients has had this problem recently. To resolve this problem try the following as it worked for him.
1./ Ask the Hosting provider to make sure both ASP.NET 2 or 4 are assigned to your site.
2./ Make sure all directories under the site have modify permissions for the user controlling ASP.NET Apps i.e. Either Network Services or Application Pool Iden y (IIS7 or Above)
3./ Download your DB file if you are using SQL Express then do this via FTP and install SQL Management studio express from Microsoft site and open the database to verify the integrity of the file.
Hope that Helps If you are still having problems let me know the name of the site and I will see if I can trace your error for you.
This and many other errors can suddenly happen when your hosting provider does an update on IIS or the server software. Or if they changing the security configuration. I know this from Experience and with our servers I am always having to monitor what our clients are using to make sure they do not have down time from these issues.
Thanks
Paul
Palatine Webpartners