I wasn't aware of any customizations added to this.
They said they were on record X.
They hit "BLOCK" checkbox by accident.
Navision autmatically moved on to the next alpha-numeric record. There is no opportunity to uncheck it.
I tested it on an unused item and I cannot get to a point where, once checked, I can get that record in to the Item Card screen. So, I see no way to ucheck the checkbox.
It sounds like I have to look at a customization already on this screen before I was hired, if I understand you correctly.