Just experienced the same error. To fix it, first check if your datasource groups and fields are correctly defined
grpContactSelector (non-repeating group)
Person(repeating group)
DisplayName (field), AccountId (field), AccountType(field)) (Fields can be elements or attributes, doesn't matter, but make sure fields are under Person group).
Then, follow the remaining steps exactly...
1. Remove the control both from the form and the control pane via "Add or Remove Custom Controls" link at the bottom of the controls tool box window.
2. Add the control again via the aformentioned linke, but follow the steps carefully:
Select "ActiveX Control" option, Press Next
Select "Contact Selector", Press Next
Select "Don't include a .cab file" option, Press Next
Select "Value" a binding option, Press Next
From the FIRST DROPDOWN (not the checkboxes), select "Field or Group (Any Data Type)" choice, Press Next. Do not literally select a data type from the checkboxes, with the first option ("Select Field"). This is the error, I did.