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:
- Launch the HyperFS client
- Double-click the MDC IP address to get a listing of the exports
- Left click an export once to select it
- in the lower half, expand "Advanced"
- Expand "RPC Options"
- Modify the "NFS Server Port" from "2049" to "2050"
- Mount that export
- Repeat steps 3-7 for all exports
This is a screenshot showing the correct option being selected: