With a vSphere ESXi 5 environment , running vRanger 5.2.1 a NBD backup of a VM with an open snapshot will fail with the following error
The error message is "An internal error occurred during execution, please contact vizioncore support if the error persists. Error message: Index was outside the bound of array"
Defect is logged - currently being investigated.
Only work around for now is to commit the open snapshots.