iMac 2009 Bluetooth problems

I just received my new iMac: 2.93GHz, GT130

I'm trying to connect to my Apple wireless aluminium keyboard but am having problems.

The keyboard still works fine with my other Macs, and has the latest firmware update.

However with the new iMac, the following happens (2 windows displayed - the Bluetooth Prefs and the Bluetooth Setup Assistant):
1. When I browse, Bluetooth Setup Assistant will find the keyboard.
2. I'm asked to enter a pairing code, which I do.
3. In the Bluetooth window, the keyboard shows up as paired and connected, but in the Setup Assistant window the little dial is still spinning.
4. After a few more seconds the message "The pairing attempt was unsuccessful" comes up in the Setup Assistant window and the keyboard disappears from the Bluetooth window.

I've restarted, reset PRAM, reinstalled the system. None had any effect.

Is this a known issue with the new iMacs, or does anyone else have any suggestions of what to try before the last resort of sending the machine back for a replacement?

Thanks in advance for advice.

After 3 days of this I've now connected and paired successfully.

I'd previously tried shutting down and unplugging the power cord from the powerpoint, but this time I actually pulled out the power cord from the back of the iMac and reinserted it.

Thanks Apple Support...I was quite surprised, hopefully this isn't just a temporary coincidence.