have you ever tried to figure out, that vm has memory reservation set and due to this you can't increase vRAM on it?
not that I'm aware of. If you don't have memory hotadd enabled, then the VM has to be shut down to change the RAM configuration.
Can you try manually in vSphere web client?
What's the exact error message?
as my server is production one, I am not able to provide today error, but here is error msg from my try over Orchestrator:
An unexpected error was received from the ESX host while powering on VM vm-36204.
Module MemSched power on failed.
An error occurred while parsing scheduler-specific configuration parameters.
Invalid memory setting for FPT: memory reservation (sched.mem.min) should be equal to memsize(8192)