A strange problem that fails to be generated but can be debugged

Today, when I was writing a program, I found a strange problem.
After a webpage is compiled and translated, it prompts that the context does not have a gridview, which has been declared on the page and can be accessed normally in the CS file of IDE. but it cannot be compiled. if this error is ignored and compilation continues, you can continue. however, the website cannot be published if compilation fails.
Later, I accidentally discovered the problem. I copied a copy of this page. The default file name is "Duplicate xx. aspx and recovery xx. aspx. CS ", and in the @ page attribute, codefile is still the default" XX. aspx. CS ", it is for this reason that the gridview is in XX. ASPX page declared, in XX. aspx. the CS page can be accessed normally. during compilation, the compiler found that the "Replica xx. the ASPX page does not contain the declaration of the gridview, so it prompts that the grirview cannot be found in the context. remove or remove the duplicate from the solution.
I don't know if the problem is correct. It is a temporary solution.