Backup Failure

Hi all

I have a backup problem:

2013-03-03 17:59:11.51 spid223   BackupMedium::ReportIoError: write failure on backup device 'H:\file.BAK'. Operating system error 112(error not found).
2013-03-03 17:59:11.51 spid223   Internal I/O request 0x55D6B6E0: Op: Write, pBuffer: 0x0B130000, Size: 983040, Position: 202529576448, UMS: Internal: 0x103, InternalHigh: 0x0, Offset: 0x27B41600, OffsetHigh: 0x2F, m_buf: 0x0B130000, m_len: 983040, m_actualBytes: 0, m_errcode: 112, BackupFile: H:\file.BAK
2013-03-03 17:59:11.53 backup    BACKUP failed to complete the command BACKUP DATABASE [dbname] TO  DISK = N'H:\file.BAK' WITH  INIT ,  NOUNLOAD ,  NOSKIP ,  STATS = 10,  NOFORMAT