c# sql visual studio 2019

Question

I accidentally deleted the main window .aspx in working c# in webforms application then it started showing this error how can I fix it.

Severity Code Description Project File Line Suppression State Suppression State
 Error      
Unknown build error, 'Object reference not set to an instance of an object.'    Test

Answer 1

Have you added the file to your solution? Adding it to the original folder might not be enough. Go to solution explorer and do the following:

• Click "Show all files"
• Right-click on the file you want to include.
• Click "Include in Project"

Once you've done this, try to build the solution and see if it gets rid of the error. If that doesn't work, I'd probably say your issue lies elsewhere.