Issue with remote execution of sqldatacompare

We are calling sqldatacompare via powershell remote execution.
If I log as the user were are coming across as - it works.
If we call the powershell script (again as the same user) we get an access denied:

System.Management.Automation.RemoteException
Unhandled Exception:
System.UnauthorizedAccessException: Access to the path is denied.

I personally think it is because the user coming across needs "Logon as a Batch Service" or "Logon as a Service" rights but not sure right now and wanted to ask a question first.

My question is - which path is it complaining about?
Is it where the project file is (i.e. ..\config\sdc)?
Is it where it wants to export files to (i.e. ..D:\temp\RedgateCompare)?

My other question is - is there some verbose switch we can use - we tried /verbose in PowerShell but got the same error.

Is there some special diagnostic switch we can use that will tell us more?
I know it is access denied - but I don't know on what

<Error stuff>

Version of SQL Data Compare Command Line:

 V14.1.7.14336

 Command Line is:

& 'C:\Program Files (x86)\Red Gate\SQL Data Compare 14\sqldatacompare' /Server1:. /Database1:'PRODDB' /Server2:. /Database2:'PRODDB_DELTA' /Export:'D:\Temp\RedgateCompare' /Project:'C:\Config\sdc\PRDODB.sdc' /Verbose /Force /MaxTransactionSizeMB:300 2>&1

Error:

System.Management.Automation.RemoteException

Unhandled Exception:

System.UnauthorizedAccessException: Access to the path is denied.

   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

   at System.IO.Pipes.NamedPipeClientStream.Connect(Int32 timeout)

   at RedGate.Ipc.NamedPipes.NamedPipeEndpointClient.Connect(Int32 timeoutMs)

   at RedGate.Ipc.Rpc.RpcConnectionProvider.TryGetConnection(TimeSpan timeout)

   at RedGate.Ipc.ReconnectingConnectionProvider.ReconnectionWorker()

   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)

   at System.Threading.ThreadHelper.ThreadStart()

 

Exit code: -532462766

 

Error comparing databases

Data           : {}

InnerException :

TargetSite     :

StackTrace     :

HelpLink       :

Source         :

HResult        : -2146233087