关于一个错误报告的问题
--------------------Configuration: 1 - Win32 Debug--------------------
Compiling...
1.cpp
F:\1.cpp(7) : error C2555: 'CTestApp::InitInstance' : overriding virtual function differs from 'CWinApp::InitInstance' only by return type or calling convention
c:\program files\microsoft visual studio\vc98\mfc\include\afxwin.h(4031) : see declaration of 'CWinApp'
Error executing cl.exe.
1.exe - 1 error(s), 0 warning(s)
这个错误是什么原因