Existing Functional SureBackup Job Failure
A simple solution to resolve "OS did not boot in the allotted time" is to increase the Maximum Allowed Boot Time to a very high value. This will likely make the error stop occurring, as it will give the VM as much time as it needs to reach a stable state. However, it will mask any subtle on-boot issues that may be occurring or occur in the future. The Maximum Allowed Boot Time serves two purposes, it controls how long SureBackup will wait for the VM to stabilize, and it can help to alert the backup admin of potential on-boot issues that may be affecting the original VM that was backed up.
The best course of action is to adjust the Maximum Allowed Boot Time to a sufficient value for the VMs being tested to boot consistently. The default Maximum Allowed Boot Time values are viable for most environments but may require some adjustment to find the correct value for each VM in each environment.