Are you using a USB drive?
There was a thread recently where it was suggested that ripping using a USB drive wouldn't work. Something about Windows/Mac/Linux JRiver not being able to take full control of the drive to support secure ripping. But the thread could have just been about the JRiver Id. It was suggested that an internal drive would be required. I don't know if that is fact though. (Is this CDs?)
Anyway, if ripping isn't available in JRiver MC, is it available with other software? If you can confirm with other software that the drive is seen and available to rip a disc, that would narrow down the potential issues.