CreatePCurve returns null

Hello All!

now i am tring to create pcurve (parametric curve or curve
projection onto surface) from 3D-curve (e.g. from line).

The following is pascal (Delphi) variant of code:

var v_props, v_knots, v_ctrlPtCoords: variant;
...
val := iCrv.ConvertLineToBcurve (v_start, v_end);
v_props := VarArrayCreate([0,1], varDouble);
v_props[0] := val[0]; //DimensionControlPoints and Order
//in this case: DimensionControlPoints=3 , Order=2
v_props[1] := val[1]; //NumCtrlPoints and Periodicity
//in this case: NumCtrlPoints=2 , Periodicity=0

v_knots := VarArrayCreate([0, NumCtrlPoints+order-1], varDouble);
v_ctrlPtCoords := VarArrayCreate([0,
NumCtrlPoints*DimensionControlPoints-1],
varDouble);

for i:=0 to (NumCtrlPoints + order) -1 do
v_knots := val[i+2];
sz := i+2;
for i:=0 to (NumCtrlPoints * DimensionControlPoints) -1 do
v_ctrlPtCoords := val[i+sz];

pCurve := fModeler.CreatePCurve(fSurface,v_props,v_knots,v_ctrlPtCoords)
as iCurve;

and here : (pCurve == nil) ?!?!
why? could You help me please?

Thanks.
Vasilii Sorokin