ref 530d Intermittent Staring Problem Help Please

Hello,
As subject, I have a 2001 530d that sometimes won't start,
seems ok first thing in the morning, but when my wife takes my daughter to
school, It has on a few occasions decided not to start, the engine has
probably been running for about 5 - 7 mins. Once the car has been left for
a while it will start ok.

Could it be Immobiliser Problem or somebody said to me Solenoid on Fuel
Supply

Any advice please

thanks

Colin Bowler