Making a 'New Order' problem

[fermain]

I have one product where there is a choice of Medium or Large. When I input a telephone order with this product on the New Order page I get the error 'An invalid arguement was encountered' when I click the confirm button.

The New Order system works fine for any other product. Any thoughts?

[Noncents]

Any joy with this one? My clients had the same issue and I can't find any other mention on here.