I believed most of system administrator and vmware administrator experiencing these issues when cloning a virtual machine on ESXi vCenter server.
Cloning process fails at approximately 90% with error message:
Number of virtual devices exceeds the maximum for a given controller
1. Make sure there are no CDs or ISOs mounted to the VM
2. Make sure that the source machine has been Power off before the clone to get a clean copy.
3. Clone the virtual machine again, without selecting the Edit Virtual hardware (Experimental)option.