The value for the 'compilerVersion' attribute in the provider

Hi Folks,
I recently wrote one application (Membership and sql server 2008) it workied fine on my dev machine. 
When i published i staretd getting following error.
i tried to adding  <trust level="Medium" /> in my web.config. no show. 
then i tried by removing  targetFramework="4.0" from web.config. but my application was not accible then.
then i tried changing it to 3.5 no show.
any ideas folks. 
Server Error in '/Demo' Application. -------------------------------------------------------------------------------- The value for the 'compilerVersion' attribute in the provider options must be 'v4.0' or later if you are compiling for version 4.0 or later of the .NET Framework. To compile this Web application for version 3.5 or earlier of the .NET Framework, remove the 'targetFramework' attribute from the <compilation> element of the Web.config file. D ...