comdlg32.dll is not a COM DLL and cannot be registered.
One way to confirm this for yourself is to run this command:
dumpbin /exports comdlg32.dll
You’ll see that comdlg32.dll doesn’t contain a DllRegisterServer method. Hence RegSvr32.exe won’t work.
That’s your answer.
ComDlg32.dll is a a system component. (exists in both c:\windows\system32 and c:\windows\syswow64) Trying to replace it or override any registration with an older version could corrupt the rest of Windows.
I can help more, but I need to know what MSComDlg.CommonDialog is. What does it do and how is it supposed to work? And what version of ComDlg32.dll are you trying to register (and where did you get it)?