ABPhysicsEngine - AddForce vs AddGlobalForce

Hi,
I cannot get AbParticle1.AddForce(AbForce1) working.
What am i doing wrong ?

Works : ( particle falls down )
' AbParticle1.AddForce(AbForce1)
PhysicsEngine.AddGlobalForce(AbForce1)

Does not work : ( particle stands still )
AbParticle1.AddForce(AbForce1)
' PhysicsEngine.AddGlobalForce(AbForce1)

Attached is my simple source.
Thank you very much.
( I know this will be embarrasing )