I made a virtual appliance a while ago for a client everything seemed to be working, but there was a slight problem with it, since it was exported in ova and imported back to a ESXi 5.0 it didn't work because of the virtual hardware version. I spent some time figuring what the correct version should be and here is what I found:
virtualHW.version = "4" # essential for ESX 3.5
virtualHW.version = "7" # essential for ESX 4.0
virtualHW.version = "8" # essential for ESX 5.0
virtualHW.version = "9" # essential for ESX 5.1
You will find the hardware version in the VMX file afterwards you can export it back to OVA. Let's cross fingers and hope it works this time.