Error connecting to undo manager of source file

Issue

Above error message appears when user tries to debug a web application in Visual Studio 2005.

Solution

This error message can be fixed by simply deleting the designer file (aspx.designer.cs/aspx.designer.vb) of the page that is causing the error; you can get the page name from the complete error message you are receiving.

To recreate the designer file, right click on the page ASPX file and click on Convert to Web Application.

That will fix the problem.