Registering fail

I got to install the client application in the 9x client PC. During the installation, there is an error occurred that “RCAPIOCX.OCX” failed to register. I tried to uninstall the client application and delete the RCAPIOCX.OCX from the window/system directory. When I re-install again, the error of failure to register is always appeared. I used run command “regsvr32 /u RCAPIOCX.OCX” to unregister, but the return value is error. How can I unregister the OCX? Any thing that I can proceed. Please advice. Thank you.