I came across this error because I had the wrong .NET version (v2.0 instead of v4.0) configured on the web site application pool. I fixed it this way on Windows Server 2008 R2 and IIS 7. I’m pretty sure the instructions apply to Windows Server 2012 and IIS 8 as well:
- Press keys Windows+R to open the Run dialog, type inetmgr and then click OK. This opens the IIS Manager.
- In the left treeview, locate the Sites node and find the Default Web Site node under it (or the name of the site where the error message appears).
- Right-click the node and select Manage web site -> Advanced settings…. Note the name of the value Application pool. Close this dialog.
- In the treeview to the left, locate and select the node Application pools.
- In the list to the right, locate the Application pool with the same name as the one you noted in the web site settings. Right-click it and select Advanced settings…
- Make sure that the .NET Framework version value is v4.0. Click OK.
This doesn’t apply if you’re running an older site that actually should have .NET v2.0, of course 🙂