User receives ERROR_BAD_EXE_FORMAT on 64-bit Windows

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1

The most common problems with 32-bit applications on 64-bit Windows involve image mismatch. An image mismatch occurs when a 64-bit process tries to load a 32-bit DLL or a 32-bit process tries to load a 64-bit DLL. Image mismatch errors that cause a worker process to fail during startup are logged in the Windows Events log as 0xC1: ERROR_BAD_EXE_FORMAT. Image mismatch errors that do not cause the worker process to fail during startup are logged in the IIS log files as Win32 error 0xC1: ERROR_BAD_EXE_FORMAT. To remedy these errors, configure IIS to launch worker processes that are the same bitness as your applications. For information about how to configure IIS to run 32-bit applications on 64-bit Windows, see Configuring IIS to Run 32-bit Applications on 64-Bit Windows. For more information about running 32-bit applications on 64-bit Windows, see Running 32-bit Applications on 64-bit Windows.