I am not an audio engineer, just bought a USB Cassette plater (Super USB Cassette Capture) to digitise old mix tapes but keep on getting:
Error opening audio device
Error code: 9986 Internal PortAudio Error
Please help! 
No-one has ever been able to get one of those things to work reliably on Mac.
The only solution is to get a Behringer UCA-202 (or similar) and a cord to go from the headphone output of the cassette to the audio input of the Behringer.
– Bill