I ran into this error message when importing a vm that was created on VMWare workstation to vSphere ESXi 5.5. I got this message:
To create a workaround for this, you'll need to modify the .vmx text file that is on the ESXi server.
First you'll need to turn on ssh access to the server.
Under Configuration -> Security Profile -> Properties
Check the SSH Server to allow incoming connections and start the service.
Next SSH to the ESXi server with your credentials.
cd to the datastore of your vms.
cd to the VM image. Use "Quotes" if there are spaces in your vm name.
cd "Win 2008 Serv (DB3)"
Next edit the .vmx file
vi "Win 2008 Serv (DB3)"
Look for virtualHW.version
.encoding = "UTF-8"
config.version = "8"
virtualHW.version = "10"
change the virtualHW.version from "10" to "8"
Save the changes.
Go back to the vSphere GUI.
Power off the VM image. Then right click and remove the VM from inventory.
Then go back to your SSH connection and reregister the image to bring it back online with the new changes.
Here's the command to reregister.
vim-cmd solo/registervm path-to-vm/VM.vmx
vim-cmd solo/registervm /vmfs/volumes/53bc3b04-5e592400-c6f3-f8bc124b4cea/Win 2008 Serv (DB3)/Win\ 2008\ Serv\ \(DB3\).vmx
It should editable after that.