GVM1219E Your selection of virtual machines has caused the backup task definition to require `count` characters, which exceeds the 512 character limit. Either create multiple backup tasks with less virtual machines per task, or select the newly added virtual machines checkbox and choose entire hosts with no more than a few unselected VMs.

Explanation
The backup task definition has a 512 character limit, and the total number of characters for the selected items exceeds this limit.
Administrator response
Create multiple backup tasks with less selected virtual machines per task, or select the newly added virtual machines checkbox and then select hosts instead of individual virtual machines (you can de-select a small number of virtual machines per host if desired.)