3228911 - backup failed with error message "Bad file number"

The following error message is in the backupserver errorlog file :

Sep 13 15:30:05 2021: A00: SYBMULTBUF ERROR: Error writing to archive device /dump/ECPDR1.dmp. Attempted to * 65536 bytes, 21504 bytes were written.
Sep 13 15:30:05 2021: Backup Server: 4.145.2.22: [3] Error for database/archive device while working on * device '/dump/ECPDR1.dmp'.Error writing to archive device /dump/ECPDR1.dmp.Attempted to * 65536 bytes, 21504 bytes were written.
Session: 0x60000000006e1c60 * id: 0 Event: *

Sep 13 15:30:07 2021: bs__discevent: DISCONNECT Event handler called.
Sep 13 15:30:07 2021: bs__discevent: DISCONNECT Event handler called.
Session: 0x60000000006e1c60 * id: 0 Event: EXIT_DEV

Sep 13 15:30:07 2021: Backup Server: 4.141.2.21: [16] The 'ioctl' call failed for database/archive device 
while working on * device '/dump/ECPDR1.dmp' with error number 9 (Bad file number). 
Refer to your operating system documentation for further details.
Sep 13 15:30:07 2021: Backup Server: 4.15.2.2: Label validation error: seek to trailer labels failed.

SAP Adaptive Server Enterprise version : 16.0 SP03 PL05

"load database"    'ioctl'   "Bad file"   , KBA , BC-DB-SYB , Business Suite on Adaptive Server Enterprise , BC-SYB-ASE , Sybase ASE Database Platform (non Business Suite) , Problem