Update billing on distribution not allowing change to the business activity field.

When we try to add a business activity to the Charge account under billing and Del in RSSP we get the following message.

• No matches found. Try again or go back and enter a combination in the Charge To field.

Select Billing and click the … and select "edit"

When I select "enter charge account number".

I can make the change by just over writing the number in the fields

but when we use the expanded search box it will not let us change it.

is this because it is not a fixed chart of account combination?