Could be a few things.  Is this on a local or remote machine?  Your either missing some folder/files or your web.config file is not properly configred (ie. Database, Framework etc.)  If this is a remote machine, post the url also copy the ENTIRE error report for us.

Thx

-Mark W.

This may not suffice here because its referring to a lower level within the .NET 2.0 Framework.  Whenever someone is using DNN there are numerous ways someone can get an error like this because DNN (vb.net) is on a little higer level and there are many ways of installing it on many environments.  That is why its important for everyone to provide as much information about the DNN Version, Windows Server, Database, Framework, Method of installation, Security settings etc. in order for someone to thoroughly answer their question.  Otherwise we would all just be playing the guessing game.