DPM 2012 R2 cannot attach the agent on a workgroup computer

In case you have installed the DPM agent manually, on a workgroup computer and you are facing issues when trying to attach it to the DPM server:

At first, check the following steps:

- Does pinging the Hostname from both sides work?
- Can you try to use the FQDN instead of the hostname for the setdpmserver command ?

Then, backup your Hosts an LmHosts files (located in the %SystemRoot%\System32\Drivers\Etc folder on a Windows computer) from both the DPM and the protected server.

Then, try to add the NetBIOS name of the DPM server, to the Hosts file on the affected remote server.
The refresh the DPMRA service and check the issue again.

If that is not enough (after monitoring the issue for some time) you need to update the Hosts file, on both servers > refresh the DPMRA service on the Protected server >
check the agent status on the DPM console..

If that fails too, then you will need to use the LMhosts file of the protected server:
Rename the extension from .Sam to simply lmhosts (you need to back-it-up first) > then add the static entry for the DPM server > then start the network discovery services.
Check the issue again.

More information you may find here:
Installing Protection Agents on Computers in a Workgroup or Untrusted Domain - https://technet.microsoft.com/en-us/library/hh757995.aspx

After installing the agent, you need to run SetDpmServer and specify the local user credentials which would be used for authentication.
A local user account will be created and the DPM protection agent would be configured to use this account for authentication.

Syntax:
SetDpmServer.exe -dpmServerName <serverName> -isNonDomainServer -userName
<userName> [-productionServerDnsSuffix <DnsSuffix>]

If it fails on these ways too, you will need to collect the DPM logs (msdpmcurr.errlog or, the log from the time you have the last repro) so we can investigate further.