CMS Compilation Error

ERROR: Argument not specified for parameter 'key' of 'Public Default Property Item(key As TKey) As TValue'.

CMS Object: /smte/Ticketing/Eintrittsticket.htm/Script
Line Number: 10

Source Code:

Line 7:     
Line 8:
Line 9: Public Sub OnModifyProductSelection(ByRef lstPreisInfo As Dictionary(Of Integer, BrGruppePreisInfo))
Line 10: lstPreisInfo().Selected = True
Line 11: End Sub
Line 12:
Line 13: End Class
Line 14:
Line 15: End Namespace