Microsoft Surface Ergonomic Keyboard pairing issues I recently bought a Microsoft Surface Ergonomic keyboard. It paired with my mid 2011 MacBook Air running High Sierra straight away. However, when I try to pair it with my mid 2011 iMac (also running High Sierra) it just won't pair. 
It occasionally recognises a new device, although the MacBook picked up immediately that it was an 'ergonomic keyboard,' when the iMac recognises it it identifies it as unknown device with a serial number 00-00-00-00-00. It then asked me to enter a code, I've tried the generic 0000 as well as 1234, and even 00-00-00-00-00, but it continually fails to connect.

I've also tried - and failed- to use the 'set up a new keyboard' function in Bluetooth preferences. That button only appears sporadically, but when it has I've tried to 'press the button that appears to the left of the shift key' to identify the keyboard, but this doesn't work either.

I've about come to the end of ideas, anyone out there have a similar experience and managed to find a solution?  Grateful for any help received.
The issue was with the version of Bluetooth. The built-in version (2.0, I believe) wouldn't configure with the keyboard.

I've since bought a Bluetooth 4.0 Dongle (cost about £12) and I can now use the keyboard. It's a bit of a faff, had to download a Bluetooth developer tool from Apple and I now have to manually switch from the internal Bluetooth to the dongle before I can use the keyboard.

Thanks for all your suggestions, though, and hopefully anyone facing the same issue now has a solution.

Kieron