[ljguitar]

Hi GG (Steve)...
I have an H4 that was doing what yours was today - and I recently had upgraded my Mac to system OSX 10.5.6

So I went here...
http://www.zoom.co.jp/english/download/software/h4.php and it told me my system on my H4 was not current (I read the update list and compared it)

When you turn on the H4, it tells you which version of the software you have in the upper left hand corner of the screen (quite short by the way).

I then went to the page I listed and downloaded the appropriate upgrade (there are 4 options, so you must download the proper one to install).

I followed the directions, installed it, rebooted to be sure the upgrade was correct, and then shut off the power on the H4...
Then I plugged in the USB cable
Selected Audio I/O
Selected 'Connect'
Selected 'mic'

Launched Garage Band and told it new song
- Preferences H4 Input
- New Track (Real instrument, basic vocal)
- Turned off the metronome
- Selected record in the track, and I had an interface connection...(meter moved in the track when I tapped the H4 mics)
- Recorded a short track
- Created a 2nd track and overdubbed it...
- Checked and played with both tracks - and it all worked as expected

I suspect you may need to check your H4 version against the latest one listed on the page...latest is 2.30

Hope this helps...