Unable to add AVE to DPA

When attempting to add an Avamar Virtual Edition server to Data Protection Advisor monitoring it fails with

Performing tests for EMC Avamar:
Test failed! Error :
[collector dpa-as on port 3741 returned an error processing command: Unable to connect to server]

The agent log just reports the same error.

We have tried the 'default' credentials (which uses the 'viewuser' builtin account I believe) and also a newly created 'dpa' user, the result is the same.

The DPA server is able to ping the Avamar system and connect to it via telnet on port 5555.

We have also run the rest for the 'viewuser' account described here and that also passes: https://emcservice.force.com/CustomersPartners/kA2j0000000R4gHCAS