Enterprise upgrade to Domino Lotus Notes 8.5, clients first, servers at 6.5 now, 8.5 to come. Clients sporadically receive "Cannot execute the specified command" error when clicking on Send in email. Email is sent, but msg pops up and email window stays open, needs to be closed manually. Deleting cache.ndk prior to launching client, temporarily stops reoccurrance, until next time client is started. Errors are machine / client specific, do not follow user to 2nd client.