Cannot backup data?

[corbint]

Attempting to backup at the domain level in the control panel, and keep getting this error message :

Error: Unable create backup session: agent_extract: execve failed for /usr/local/psa/admin/sbin/agent_extract: No such file or directory

System error 2: No such file or directory


How can I get the backups to work? OS is FreeBSD with Plesk 8.0.