The /I switch does not seem to be needed according to:
[
how-to-register-an-activex-control]
If the .OCX file is not located in your windows/system32/ folder you must add the file path before the filename.ocx
Oh, and don't forget to run with administrator rights !
You can also try:
cd \Windows\SysWOW64
Regsvr32 /u {Filename.ocx}
Regsvr32 {Filename.ocx}