The Invalid List Box widget error is issued in the following situations:
'Selection Attribute' must be filled in with a Boolean attribute in <List Box> widget: you have a List Box widget and it won't be possible to determine which values are selected or not, because the Selection Attribute property is not set properly.
Edit this List Box widget and change the Selection Attribute property to an attribute whose data type is Boolean. How?
'Source Attribute' must be filled in with an appropriate attribute in <List Box> widget: you have a List Box widget and the property that indicates which attribute is to be displayed is not correct. This situation occurs, for example, when you delete the record attribute that is being used as the source attribute, or when the attribute is of the Binary Data data type.
Edit this List Box widget and change the Source Attribute property to a suitable attribute. How?
Clicking the symbol will take you directly to the invalid List Box widget.
About List Box Widget | About Error Messages