Audacity for cassette to mp3 conversion error

Hi everyone,

I am using Audacity 2.3.2 and have been trying to convert cassette recording to mp3. I have a Retround USB tape to MP3 player.
I am using Mac OS X El Caption 10.11.6

What happens is, when I try to record, this error message comes up:

Error opening recording device
Error code: 9997
Invalid sample rate.

Any ideas how to fix this?

Many thanks!