The parameter you are referring to is the 2nd parameter in the SendRemoteControl() method. The parameter is named IanaOemNumber, and it's of type Uint32 (uint for short in c#). Tracing this a bit deeper, the SendRemoteControl() method actually calls the SendRemoteControlEx() method on a separate thread, which calls the Put_BootSettingsData() method, passing the OEM parameter to it. The Put_BootSettingsData() method uses the OEM parameter to determine whether or not Serial-over-LAN is supported, and sets a flag based on this for the next reboot. Beyond this, I'm having a hard time finding anything about the error message you posted. What's really odd is that, within the ManageabilityStack, I don't see any other references to the UNSUPPORTED_OEM_NUMBER enumeration value, which is actually defined in the AmtSystem.cs source file. The value is defined, but never used anywhere, so I'm not quite sure how you're being returned this code.
You know what might help, is if you posted a screenshot of the error message you're getting in the PowerShell console. Could you do that for me?
I honestly don't know exactly what the IanaOemNumber parameter does, although when I originally wrote the PowerShell code, I probably just randomly plugged in a hex value of 0 to see if it would work, and it probably did for me at the time. Hopefully we can get to the bottom of this, though