The maximum a VM thats configured for hardware Level 9 is 32vCPU's per VM....if you are getting a message about a VM with 8 vCPU then you have not completed a hardware upgrade on the virtual machine after upgrading to ESX 5.1 as the limit on esx 4.1 is 8 vCPU per VM
PS - the license has nothing to do with the number of vCPU you can assign to a VM (except at the lower ESX license levels)
Also your configuration does not follow best practice at all as you are dedicating every Core on the server to the virtual machine and leaving nothing to the Hypervisor That will cause you performance problems
Are you actually sure that system is gonig to use at least 80% of the 24 cores all the time? If not, you are gonig to find performance is worse then if you actually sized the VM for the workload since having too many IDLE cores in a VM can cause excessive CPU ready times...