First, make sure you're not connecting through any USB hub. Only direct connections to your Mac will do. Try a different USB port too.
New Macs have issues with PocketMac. Sometimes it just won't work with the newer Macs, especially the Intel Macs. An alternative is Mark/Space's Missing Sync
. It's not free like PocketMac but *sometimes* Missing Sync works when PocketMac does not. It's $40, but if it's the only solution that works it might be worth the cost. Or you could try to hold out until the Mac version of BlackBerry Desktop Software is released some time in September.