Unable to parse xml element 'Envelope'

I used ovftool (1.0 running in a RHEL 5.2 VM) to create an ovf of a powered off RHEL 5.1 VM.  All was successful and I can probe the OVF without issue.  However, when I try to import it as a virtual appliance using Virtual Center 2.5 Update 5 I receive:

An error occurred while parsing the OVF descriptor:  Unable to parse xml element 'Envelope'

I've attached the ovf file.

Any ideas?