Hello,

I am trying to upgrade a copy of Umbraco from 6.1.6 to 6.2.5

• I've applied the changes to the .config files to the new versions
• I've changed the version in web.config to the right version
• I've dropped the new files onto the right place in the codebase

Front-end works (after I got rid of some obsolete code), Back-end login page works, and if I try to go to a specific frame e.g. /umbraco/dashboard.aspx?app=content# then that works.

If I try to just go to /umbraco/ and log in, I get redirected to a yellow screen of death:

Server Error in '/' Application.

Method not found: 'System.Collections.Generic.IEnumerable`1

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.MissingMethodException: Method not found: 'System.Collections.Generic.IEnumerable`1

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[MissingMethodException: Method not found: 'System.Collections.Generic.IEnumerable`1

[TypeInitializationException: The type initializer for 'umbraco.BusinessLogic.Actions.Action' threw an exception.]
umbraco.BusinessLogic.Actions.Action.GetJavaScriptFileReferences() +0 Umbraco.Web.UI.Umbraco.Umbraco.RenderActionJs() +83
Umbraco.Web.UI.Umbraco.Umbraco.Page_Load(Object sender, EventArgs e) +1690 System.EventHandler.Invoke(Object sender, EventArgs e) +0 Umbraco.Web.UI.Pages.BasePage.OnLoad(EventArgs e) +19
System.Web.UI.Control.LoadRecursive() +71
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3178

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34249

Any idea where I can even start looking to fix this?