X5 Did not Start - Preheating on OBC

[demondali]

Yesterday morning when trying to start my X5 it just wouldnt start. I had a previously unseen message on the OBC appear "PreHeating" I tried to start it a couple of times and it just would not fire up.
I assumed that that the battery may have gone flat but having just done an hour drive the night before i was shocked.
Its a 2005 E53 3.0d X5 had it from new and never seen this message or had any problems starting it up before.
The temperature was about 1 degree celcius however i have driven it in the snow and started it up on colder mornings before.

Anyone know what might have caused this?
Anyone had similar issues before?

Its funny how this morning it started up without any problems and its back up and running as normal!

Should i be concerned? or is this normal... i know some of you experience much more colder climates that us Brits!