Oracle Message ORA-01918 - user string does not exist

ERRORuser string does not exist
CAUSEUser does not exist in the system.
ACTIONVerify the user name is correct.

499663Manually upgrading the Oracle database
313087INST: 3.1I SR1 R/3 Inst. on UNIX - Oracle
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375184INST: 4.0B SR1 + 40B_COM Kernel R/3 on UNIX - Oracle