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ORA-01173:

data dictionary indicates missing data file from system tablespace
Cause: Either the database has been recovered to a point in time in the future of the control file or a datafile from the system tablespace was omitted from the create control file command previously issued.
Action: For the former problem you need to recover the database from a more recent control file. For the latter problem, simply recreate the control file checking to be sure that you include all the datafiles in the system tablespace.