Maybe, but I found other way and run smootly

Local nX, nY
IF nButton=1
nX = nXCoord + This.Left - this.xstart
nY = nYCoord + This.Top - this.ystart
This.Move(nX,nY)
ENDIF

With your code, the window make strange movements.
Other thing than I found is: if you set the Enabled property of controls to .F. you still can move the form in that point (any part of the control)

Tanks again!