oracle error- ORA-00394: online log reused while attempting to archive it

Oracle error

ORA-00394:	online log reused while attempting to archive it
Cause:	It has been detected that an online log that is being archived has been reused
Action:	Cannot archive the logfile anymore since it has been overwritten

oracle error- ORA-00393: log string of thread string is needed for recovery of offline datafiles

Oracle error

ORA-00393:	log string of thread string is needed for recovery of offline datafiles
Cause:	Log cannot be cleared because the redo in it is needed to recover offline datafiles. It has not been archived so there is no other copy available. If the log is cleared the tablespaces containing the files will have to be dropped.
Action:	Archive the log then repeat the clear command. If archiving is not possible, and dropping the tablespaces is acceptible, then add the clause UNRECOVERABLE DATAFILE at the end of the clear command.

oracle error- ORA-00392: log string of thread string is being cleared, operation not allowed

Oracle error

ORA-00392:	log string of thread string is being cleared, operation not allowed
Cause:	An operation encountered this online log in the middle of being cleared. The command that began the clearing may have terminated without completing the clearing.
Action:	If the clear command is still executing then wait for its completion. If it terminated then reissue the clear command, or drop the log.