Virtualization software on the BE6000 hosts is always a pre-activated master serial number, but it's a different serial number for 5.x vs. 4.x.
The upgrade is NOT processed via vmware.com. If you try this you will get errors and problems.
If your ESW and UCSS contracts on BE6000 licenses are in order, should be able to get the 5.x master serial number from cisco.com Product Upgrade Tool (the upgrade SKU is R-VS5-HYP-K9-UPG=). If you download the 5.x "free ESXi download" license from vmware.com, this is usually time-limited so is only useful as a short-term fix.
Logistics may be slightly different depending on if your BE6000 license is 8.x, 9.x or 10.x, I'll let the experts comment on that angle.
