Targer Principal in Incorrect

I was unsure which subject to post this under and as could've fallen under 2 or 3.

Basically I'm running through the Managed System Config on Sol Man for an ECC QAS system.  The DEV system ran through fairly easily.  QAS is not quite the case.

Step 5:  Enter System Parameters > DB Parameters

I've used Windows Authentication (like I did with the DEV system) with an appropriate domain user and password.

But I'm seeing the following error:

SQL error 2146893022- : SQL Server Network Interfaces: The target principal name is incorrect.

Searching online hasn't thrown up much by way of a solution and my SQL knowledge is almost Zero. To be honest, I'm not even sure what it means by Target Principal!

This may well be a Windows and/or SQL issue but thought I'd try here first and see if anyone has seen this before.

Thanks.