ESXi 5.1U1 upgrade failure - OSError: [Errno 39] Directory not empty

Hello all-

just attempted to update my ESXi server from 5.1 799733 to 5.1U1 1065491.  During the upgrade the process hangs at 24% completion with the error message as above:

OSError: [Errno 39] Directory not empty: '/vmfs/volumes/3934f7e6-f070467f-afd0-f0ef312248d9/state.7173326'

I have retried a second time with the same result.  Is there any workaround?  Or can I perform a clean install and just import the VMs from the datastores without any problems?