This error can happen when the HyperFS macOS client tries to mount an export for the first time in an environment where the Scale-Out NAS Gateway (SONG) option is active.

It can be resolved by changing the NFS Server Port from 2049 to 2050, as shown below:

  1. Launch the HyperFS client
  2. Double-click the MDC IP address to get a listing of the exports
  3. Left click an export once to select it
  4. in the lower half, expand "Advanced"
  5. Expand "RPC Options"
  6. Modify the "NFS Server Port" from "2049" to "2050"
  7. Mount that export
  8. Repeat steps 3-7 for all exports

This is a screenshot showing the correct option being selected: