Hi,

I have attached a recorded video to reproduce the exception prompt

1. Drop control on web form

2. Remove it

3. Double click any .cs file.

4. Error occurred.



Thank you

Though I appreciate the video, I really need more detail here.  I saw the error, but there is no way for me to just slap a fix in here or tell you what is happening without being able to reproduce the problem.  It looks like something within your code is attempting to evaluate the ApplicationBasePage at design-time.  I see that it failed in the Extensibility assembly, but I have no way of knowing the call stack here and how this is manifesting itself without being able to reproduce it.

Could you please create a sample that reproduces this behavior?  If you can then we will have a much better chance of being able to help you here.