The replica log within the database is the SDE.GDB_REPLICALOG table. This is the case for 10.1 and for just about all previous versions of ArcSDE. Interpreting any of the numeric values in the ERRORCODE field can be painful and must be done with online searches. There are a few random Esri-published articles about specific error and HRESULT codes but they are incomplete and difficult to understand at times. A better (but not always great) way of seeing the messages associated with any replication error codes from the log is to use the "View Log" feature found within the Manage Replicas dialog box in ArcCatalog. This can be accessed by right clicking the geodatabase connection and picking Distributed Geodatabase from the menu. Once you find your replica of interest in the list, right click the replica entry to see a sub-menu with the View Log feature I mentioned before. In summary, you might find something like "-2018348485" in the ERRORCODE field of the SDE.GDB_REPLICALOG table but in the View Log dialog box you might see something like "CANNOT LOAD LOW PRECISION OBJECT WITH HIGH PRECISION DATA". This is just an example, but I think it makes the point that you'll get a bit better error reporting in ArcCatalog than directly querying the SDE.GDB_REPLICALOG table.
