Error 2 Backup too large DB - SQL

Hi all,

I have a problem with a too large DB. In the past the script the script has always worked but since a few days it returns error 2 on a given DB both for the Differential and for the transactional log.

This is the script:

OPERATION BACKUP
DATABASE $ALL
EXCLUDE master
EXCLUDE msdb
EXCLUDE tempdb
EXCLUDE model
EXCLUDE SeedDB
SQLHOST "MI-SPOINT-DB01"
NBSERVER "NBUMS-MI3.OPTIMAITALIA.COM"
MAXTRANSFERSIZE 6
BLOCKSIZE 7
OBJECTTYPE TRXLOG
NUMBUFS 2
VDITIMEOUTSECONDS 3600
ENDOPER TRUE

the backup starts correctly but when it arrives at a certain DB (about 4.5 Terabytes large) the dbbackex.exe process on the client reaches about 5Gigabytes of RAM and after a little it returns the error:

ERR - command failed: unimplemented error code 255 (255)

ERR - bphdb exit status = 2: none of the requested files were backed up.