Low oil pressure?????

[Doru]

I did an oil change about a week ago. The oil I used: GC 0wx30. 8 liters (8.5 qts).

This morning when I started her up I received this message:
"Oil pressure low" followed by: "Turn engine off and check oil level".
Which I did. The oil level was exactly where it was a week ago (1/2 mark between min & Max).

Started her up again, no warning - nothing. Drove her for 1/2 Hr, and no more messages.

What am I looking at here? Oil level sensor? Oil pressure sensor? Or is the oil pump starting going South? Or is it a glitch?

Thanks