The asp.net compilation Error Type "also exists in" different dll (Summary)

 

This problem is often encountered in projects, so we can summarize it and write it down:

 

I remembered that I added an ashx from other website projects through "add existing items" during this period, so I checked this file carefully, I found that the namespace in the cs file has been changed to the default namespace of my project, but it has not been changed in its ashx file, the namespace of the original project is retained (there is only one header declaration in the ashx file, so double-click the ashx file in VS to open its cs file directly, so it is easy to ignore this file ).

After the modification, the compilation error CS0433 is no longer displayed.