Hello, it looks like your Subaccount consists of 4 segments; one segment represents “Sales class”. 
 

We can’t just enter any letters we want in the sales class segment because sales class segment is being validated against a specific list of possible sales classes. 

Next step is to go to Configuration , Segmented Keys screen and select Subaccount to the screen.  Which segment # represents Sales Class?

Then go to Segment Values screen and select Subaccount to the screen.  Choose the Sales Class Segment Id (1, 2, 3, or 4) and you will see all the choices that are allowed for sales class.

Then return to Finance, Subaccounts and set up your new Subaccount using a correct value in the Sales Class segment.

Example showing possible values for Product Group segment of a subaccount:

Laura

Big help, thanks. Got it working