When creating a new customer we just started getting this error message - any ideas on how to trouble shoot?

This usually means the system is rejecting the formatting of what is entered in that field; use of comma or period, and so on

@Kipper Kohn that's no true Invalid value could be • There is no item with id 48344 • Item exists, but it is not available I guess there is an user event or workflow trying to set value somewhere to an item field