Sage Line 50 - unable to change translation details of a foreign currency invoice

SUGGESTED

On Sage line 50, our base currency is Euro.

 

We set up Supplier account in Sterling and entered an invoice to that account. We need to make a change to the invoice through Translations, but almost all the options on greyed out.

We have no problem changing Euro invoices entered, but not the Sterling. 

Is there a reason for this?

 

Thanks

JJ