PowerShell Remoting and WinRM PSRemotingTransportException JobFailure

I have a PowerShell script that starts up backup jobs on a Veeam server and returns the results once the job has complete.
This script works locally and remotely via Invoke-Command using a similar command to the one below.

Invoke-Command -ComputerName VeeamServer -ScriptBlock {"BackupJobA","BackupJobB" | C:\Scripts\Start-VeeamJob.ps1}

My problem is for a some backup jobs, the command executes and starts the backup job but then the WinRM session fails with the error below:

Processing data for a remote command failed with the following error message: The client cannot connect to the destination 
specified in the request. Verify that the service on the destination is running and is accepting requests. Consult the 
logs and documentation for the WS-Management service running on the destination, most commonly IIS or WinRM. If the destination 
is the WinRM service, run the following command on the destination to analyze and configure the WinRM service: "winrm quickconfig". 
For more information, see the about_Remote_Troubleshooting Help topic.+ CategoryInfo          : OperationStopped: (System.Manageme...pressionSyncJob:PSInvokeExpressionSyncJob) [], PSRemotingTransportException+ FullyQualifiedErrorId : JobFailure

When this happens the Windows PowerShell log has an "Engine state is changed from Available to Stopped" Information event under Source: PowerShell (PowerShell) | Event ID: 403 | Task Category: Engine Lifecycle
 
I have had a quick look at about_Remote_Troubleshooting at the following link but nothing jumped out at me:http://technet.microsoft.com/en-us/library/hh847850.aspx

Has anyone come across this sort of issue or could offer a suggestion? Both servers involved in the conversation are running Server 2008 R2 SP1.

Thanks,
Mark.