If you try to build a console app, for which the entry-point function is normally named "main", as a windows app, where the subsystem type on the Linker tab in the project options dialog is set to "Windows", and for which the entry-point function is normally named "WinMain", the linker will return an Unresolved external symbol 'WinMain' error.
The fix is to ensure that the subsystem type matches the entry-point function.