The following errors are observed in the target event_log with consequent out of sync:
 03/08/10 09:15 Out of sync: table - "owner"."tablename" (rid:AAAQPkAAIAADhbgABT) ORA-03129: the next piece to be inserted is required. [sp_opst_mt (for o.SID1-o.SID2 queue queue_name)/29988]
A shareplex known issue.
When there is an out of sync row on target and an UPDATE is performed on source row, the same SQL fails on the target because the pre-image of target row does not match what Shareplex expects it to be. Normally such out of sync occurence should be reported as ORA-01403 ( NOT FOUND) error but the program code treat it as ORA-03129. Shareplex generic error handling code tried to retrieve the Oracle error text for that message and it retrieved the LAST Oracle error message and logged it (even though it was the wrong message).This message has nothing to do with this latest ORA-01403 error. This issue is fixed in 7.0 and up.
If upgrade is not possible, then one needs to check the out of sync, if any, and fix them using compare or other means.