I thought I'd post my experience here so if anyone does a search they will find a solution that might work for them;
Check if you have Internet Sharing enabled.
This will prevent your system from sleeping entirely, to ensure a connection is maintained.
I've done this twice now and it took me a while to remember that was the cause! There should really be a prompt in OS X that reminds you, on enabling, that the host machine will be unable to sleep whilst Internet Sharing is active.
As a general troubleshooting tip for anyone that didn't help, try doing the standard stuff; SMC reset (turn off, unplug, plug in, reboot), and PRAM reset (hold CMD+ALT+P+R at boot, let machine 'bong' 1-3 times and release).
As a mini-tip, resetting PRAM appears to clear the association between the Mac and Bluetooth gear, so don't be alarmed if your Mac ignores your PRAM reset shortcut after one reboot, just wait until it fully boots and reboot it from the login screen and do it again.
Check if you have Internet Sharing enabled.
This will prevent your system from sleeping entirely, to ensure a connection is maintained.
I've done this twice now and it took me a while to remember that was the cause! There should really be a prompt in OS X that reminds you, on enabling, that the host machine will be unable to sleep whilst Internet Sharing is active.
As a general troubleshooting tip for anyone that didn't help, try doing the standard stuff; SMC reset (turn off, unplug, plug in, reboot), and PRAM reset (hold CMD+ALT+P+R at boot, let machine 'bong' 1-3 times and release).
As a mini-tip, resetting PRAM appears to clear the association between the Mac and Bluetooth gear, so don't be alarmed if your Mac ignores your PRAM reset shortcut after one reboot, just wait until it fully boots and reboot it from the login screen and do it again.