We were migrating a sp 2007 project to sp 2010. The web.config between the two environments were very different (mainly the version numbers). After the merging the two web.config, I was getting a plain Error 500 on the site, with no further details.
First up, open IIS, select the site, double click on the Configuration icon. If this opens, at least the web.config is fine. In my case even this did not open up, and gave an error 0x8007000D and very helpful error of empty string.
Scouting around on several websites, (the most helpful was stackoverflow.com) finally tried installing the IIS7 rewrite module (rewrite_2.0_rtw_x64.msi) and restarted IIS. Now I was able to open the Configuration Editor from IIS7.
Now hitting the site gave atleast a readable error “System.Web.Extensions not found”. The dll is installed in GAC for sure. This is for AJAX ASP.Net and apparently this has to be turned off for SharePoint 2010 which relies on .NET 3.5.
So commented out the following line:
<add name=”ScriptModule” type=”System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=22.214.171.124, Culture=neutral, PublicKeyToken=31BF3856AD364E35″ />
The site is up and running now.