Attempting to define shelf item with a key already associated with the shelf.
#6021 Run-time catchable error
Attempting to define shelf item with a key already associated with the shelf.
Additional Information
For X shelf 'Y'; For key 'Z'.
where X is either counter, stream or switch.
Explanation
OmniMark is trying to assign the key Z to a shelf which already has
item associated with the key.