Found on Metalink
Note 119547.1 : Message 'Failed to archive' in Alert.log
fact: Oracle Server - Enterprise Edition 8.1
symptom: RMAN errors when backing up archive logs
symptom: ARCHIVE LOG CURRENT command is issued
symptom: Errors appear in alert file
symptom: ARCH: Beginning to archive log# %s seq# %s
symptom: ARC0: Beginning to archive log# %s seq# %s
symptom: ARC0: Failed to Archive log# %s seq# %s
symptom: ARCH: Completed archiving log# %s seq# %s
symptom: Database in archive log mode
symptom: The redolog is archived correctly
cause: The command 'Alter system archive log current' he is forces manual
archiving of
the current log, hence the shadow process on which the command was issued will
perform
the archiving. It will archive the logfile and write messages to the
trace/alert using
the prefix ARCH.

If automatic archiving is turned on then the archiver process will also try
to archive this logfile, however will not be able to aquire the lock 'kcrrlt'
ie the lock to protect multiple arch processes from archiving the same logfile.

The failing process process will write to the trace/alert message that it was
unable to archive the logfile.

In Oracle 9i the message in the alert.log is more informative:
ARC1: Beginning to archive log# 2 thrd# 1 seq# 24
ARC1: Unable to archive log# 2 thrd# 1 seq# 24
Log actively being archived by another process

By setting the parameter log_archive_trace = 127 in the init.ora file
the archiving steps for both the shadow as well as the archiver process can be
traced.


Reference :
'ARCHIVE LOG CURRENT' causes 'FAILED TO ARCHIVE'



fix:

The command 'Alter system archive log current' is commonly used in hot-backup
scenarios. The message 'Failed to archive' can be ignored, as long as it is
followed by a 'Completed archiving' message.

Workaround:
Do not issue the command 'Alter system archive log current'.

Reference PARAMETER:
LOG_ARCHIVE_TRACE