Hi Marcelo,
Have you recently made any changes to the schema of the layers in the database OR have you added any layers to either of the database?
Have you checked the replica manager and validated the schema, you may also want to try and manually export data changes messages and import messages...
You may want to include the version of ArcGIS(9.3, 10, 10.1, 10.2, SP1, SP2) you are using and the replica type (One way, Two way, etc.)
Sol