I am getting this error message from time to time stating that Visual Studio can not connect to the Undo Manager for a given source file.
There are several solutions to this problem:
- Delete the designer file and recreate it by right-clicking on the .aspx file and chosing “Convert to Web Application”.
- Edit the .aspx file, either by typing or dragging a control into it and then recompiling. This recreates the auto-generated designer file.