problems with domain backup

[k.satirli]

im running the latest hotfixes and suddenly my domain backup stopped working for 1 domain.

the error I'm getting is:

Error in BackupState.doActivityRunner()
Traceback (most recent call last):
File "/usr/local/psa/admin/share/agent_runner/agent_runner.py", line 96, in doActivityRunner
newState = self.doActivity()
File "/usr/local/psa/admin/share/agent_runner/agent_runner.py", line 360, in doActivity
errtxt = runAgent(self, self.session)
File "/usr/local/psa/admin/share/agent_runner/agent_runner.py", line 230, in runAgent
cmd.spawn()
File "/usr/local/psa/admin/lib/python/subproc.py", line 217, in spawn
proc.run()
File "/usr/local/psa/admin/lib/python/subproc.py", line 174, in run
BaseSubprocess.run(self)
File "/usr/local/psa/admin/lib/python/subproc.py", line 158, in run
self.wait()
File "/usr/local/psa/admin/lib/python/subproc.py", line 178, in wait
BaseSubprocess.wait(self)
File "/usr/local/psa/admin/lib/python/subproc.py", line 168, in wait
raise NonzeroExitException(self, os.WEXITSTATUS(status))
NonzeroExitException: <unprintable instance object>

which doesnt help me a lot. I restarted plesk and checked any config that came to my mind and I think I did anything except rebooting.

any thoughts on what caused this and how I can solve it?

backup is working perfectly fine for other domains. domains that are much bigger.