The same problem faced by me few days back. It is because of less space on Archive disk. When u free the space then archiveing will start again autometically.

I question may arise why the Database not hanged ? when archive process fails.

The answar is

Suppose u have 3 Log groups.

when log swtich occurs and LGWR starts writing next online Redo log file, and the archive process do the archive of privios log file. On next log swtich LGWR starts writing next on line group. and Arch. process keep on tring archive log files and found no space and starts issuing archive related errors. The database will hang when all the 3 Log groups are full and archive is not done and no log group is available for Redo entries.