parserror when selecting an item from a drop-down list

Hello Tuan,

all in sudden my EB installation has started showing a pop-up with just the error "parserror" (please see attached picture) when I select an item from a drop-down list.

The drop-down is a field configured as item/quantity, that is a selectable option for the user, with a limited quantity. It has always pretty brilliantly worked, but now it has stopped. What could it be ?

Thanks !

Andrea.