problems with AutoCAD command

Hi, I have a problem with AutoCAD commands. On the TextButton1 OnClicked event I want to get a point from AutoCAD, for using it into a cylinder command. (setq p1 (getpoint)). After that I define a new point p2, which has the same X and Y coordinates, and the Z coordinate is with 20.0 smaller than the Z coordinate of p1.  (setq p2 (list (nth 0 p1) (nth 1 p1)  (- (nth 2 p1) 20.0))) .  Next, I define a real value for the diameter of cylinder (setq d_val 10.0) , and then I write the CYLINDER command, which should generate a cylinder with this defined values and points.

(defun c:aaa_Form1_TextButton1_OnClicked (/)
  (setq p1 (getpoint)) 
  (setq p2 (list (nth 0 p1) (nth 1 p1)  (- (nth 2 p1) 20.0)))
  (setq d_val 10.0)
  (command "cylinder" "D" d_val "a" p2)
)

At this moment a problem appears, saying that an AutoCAD command is wrong. If I run this LISP text without OpenDCL tools, it works.
How can I solve this?
Thanks.

Set your "Event Invoke" property on your button to = 1-Asynchronous
{2}

Also, check out the "Selections" project in the Samples folder.

Thanks Barry.now it works.