It appears that something may have changed in ESXi 4.1 build 381591 to prevent the injection of a modified SLIC table into the virtual BIOS. For several ESXi 4.1 builds (320137, 348481) the MD5 hash on the original BIOS is 261FCB72. However, with build 381591 the hash is now E55E1BC3. When I load the two previous BIOS versions into Phoenix Tool v1.85 I get no SLIC pop-up message. However, when loading the new original BIOS in 381591 into the same tool I get: Complete SLIC 2.1 (Dell QA09 1.0BNVDA) in ACPI16.COM (x1) and Pubkey and marker (2.1) (Dell QA09 ) in ACPI15.ROM (x1). Now if I boot a VM on the 381591 host and run SLIC Toolkit v3.2, it does NOT detect a SLIC table I get "Dump Error! SLIC Table not found." Next I injected my mod'd 348481 BIOS into the 381591 host, and the guest VMs still do NOT see a SLIC table. Any ideas of what's going on? I'm about at my limit of SLIC knowledge. It appears to me that VMware somehow added a disabled SLIC 2.1 table to the BIOS. Now why injecting a previously working SLIC-mod'd BIOS into the new ESXi build does work is a mystery to me. Maybe they changed the ESXi kernel to block SLIC mods? With my mod'd BIOS if I launch RW Everything v1.4 inside of a VM on the new ESXi build and look at the ACPI tables there's no SLIC tab. I do get the SLIC tab on my 341481 ESXi host. I've also found that if I power down a VM on my 341481 host that is activiated via the BIOS 2.1 SLIC, power it on the new ESXi host so that goes non-genuine, then power it off and back on the older host with the BIOS mod, Windows does not return to a genuine state and RW Everything doesn't detect a SLIC table on the older host. So something about powering on the VM on the newer host does something to prevent SLIC 2.1 to work on older host. Weird !??! Update: The root cause of the issue is not VMware, but some weird interaction between one ESXi server and the ESX BIOS tools. No need to panic!