I've used Midiox to handle sysex in Win7 64bit without problems. At least, I can dump from and to my Machinedrum and SR16 at any rate.
I've never really used Sonar's sysex sending capability, largely because I found Midiox does what I need without having to get my head round how Sonar handles sysex. And because I'm lazy.
A thought - if sysex it being sent (in effect played) from a sequencer the tempo the sequencer's running at can make a big difference to whether the data is received correctly or not. Generally speaking, slower tempos seem to make for better communication. Slowing the tempo to 60 or even 40bpm might make an improvement. Or even speeding up the tempo.......