random starting problem

[sleek_vp]

my cars an 05 vz exec and its just developed a starting issue. its happended twice within a few days- when i flick the key it cranks over for about 5- 10 secs til the starter disengages then stops (no its not like it wants to start it just cranks normally). when i flick the key again it starts normally?. what iv replaced is oil pressure sensor 2 weeks ago, fuel and air filters replaced 15k ago, plugs replaced 25k ago, its very well looked after, iv been to holden about a month ago to get 'service engine soon' fault diagnosed- this is well before existing prob started so i thought maybe the tech 2 woulda picked it up, turns out it was the sensor, im in the dark right now so if anyone has/had similar experience or knowledge plz help me out, cheers

[VYMAD]

Possibly slip key reader, although I wouldn't think it would crank at all.

Fuel pump?

[heyitsEnricoPallazzo]

Is the the immobiliser on or off when you crank the engine? There will be a flashing lock symbol in the cluster if activated.