After nightly backup VM don't start. sos

Hello.
After nightly backup VM don't wont start. Web interface - not working - first time - connection failure, now - login failed.
In SSH session:

qm unlock 300 - ok
qm status 300 - stoped
qm start 300 - without response
(host name BACKUP too)
in logs -
backup qm [56059]: <root@pam> starting task UPID:backup:xxxxx:xxxxx:xxxxx:qmstart:300:root@pam :
backup qm [56059]: <root@pam> end task UPID:backup:xxxxx:xxxxx:xxxxx:qmstart:300:root@pam : unable to read tail (got 0 bytes)
.........
disks not full.
Temporary VM 300 is located on the same nfs storage(name backup) on which there was backup error.
pvesm status - - without response

HELP!

Thanx!