Credit Note error - Item dimension and must consequently be specified

Our users have started getting this error message within the sales order, FUNCTIONS > CREATE CREDIT ADJUSTMENT NOTE

It pops up an Infolog box with variations of the following :
- Inventory dimension Classification is an item dimension and must consequently be specified
- Inventory dimension Market Region is an item dimension and must consequently be specified
- Update has been cancelled 

This has only started happening in recent weeks, does anyone have any suggestions as to how it could start popping up and how to fix it ?

There have been no Axapta patches applied to the server in over 12 months.

Any ideas of cause or a workaround would be most helpful :)

Thanks