V-79-57344-38277 - Unable to open a disk of the virtual machine.

based on the SCL (https://www.veritas.com/content/support/en_US/doc/BE_16_SCL) you need at least vmware 5.5 for use with bexec16

Just to clarify Jurgen's answer a little

Backup Exec uses VDDK components which we get from VMware. Those components are designed to support specific versions of ESXi and typically as support for the newer versions are added the older versions start to be removed from being supported by a specific VDDK package. You cannot use more than one level of VDDK on a single server and you can get errors similar those mentioned in thread if the VDDK being used does not support the ESXi version. Hence our Software Compatibility Lists are very specific about supported ESXi versions.

Once we have access to a new VDDK from VMware, we may have to change our own program to match new functionality, which will also limit any ability to possibly allow the use of a older VDDK, and we do have to implement newer VDDK to enable support for their current ESXi versions.

Basically any environment that continues to use obsolete software, whether it be the Operating Systems, Applications, Virtual System Hyper-visors, Security Products or Backup products will have to have decisions made about when everything can be updated and those decisions need to include making sure there is an awareness of which software versions might affect interactions with other active software.  In this case ESXi will need updating OR you will need to maintain an older Backup Exec version just to protect the ESXi version you are running. (if you do maintain an older version be aware of the End of Support Dates)