RegCreateKeyEx failed code 5. Access is denied.

Hi. I was trying to install Capture One - a photo editor. As I install, I get a message
HKEY_LOCAL_MACHINE\Software\Classes\.arw
RegCreateKeyEx failed code 5
Access is denied.

If I ignore this message I get the same message for .cr2 .crw .dng .erf
I aborted at this point.

If I use regedit, and navigate to this point, using Run as administrator for regedit, if I right-click .arw I get a message
.arw cannot be opened. An error is preventing this key from being opened.
Details: Access is denied.

I can successfully right-click .aps .art .asa etc
but I again get the problem on .cr2 .crw and so on

Just in case this information is useful - I have never been able to get Windows Media Player working successfully, except by regsvr32 jscript.dll
regsvr32 vbscript.dll but WMP fails to work again after rebooting (no error message).

Thanks for any help that you can give me.

Norman