Oracle Replication

We are running some Auto Replication, and the problem seems to be that some times they work, and sometimes they do not. When they do not work this is the error:

ORA-12012: error on auto execute of job 2
ORA-01004: default username feature not supported; logon denied
ORA-01988: remote os logon is not allowed
ORA-02063: preceding 2 lines from EPAB
ORA-01004: default username feature not supported; logon denied
ORA-01988: remote os logon is not allowed
ORA-02063: preceding 2 lines from EPAB
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 271
ORA-06512: at "SYS.DBMS_IREFRESH", line 413
ORA-06512: at "SYS.DBMS_REFRESH", line 171
ORA-06512: at line 1
 

We are replicating from a NT oracle Db to a UNIX Oracle db using Replication manager and Oracle 7.3. Anyone got any ideas whats going on here?  

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