vlr-dwg-reacor and running commands

I am trying to run a command from a 3'rd party application when saving the file by using the vlr-dwg-reactor. Then I get an error message "Invalid AutoCAD command". I am getting the same message if I try a regular AutoCAD command. Like in the example below. Is it not possible to run commands when using this reactor?

(defun MCE3D (reactor dwg)
;;; (command "<MYCOMMAND>")
(command "line")
(princ)
)

(if (not (vlr-reactors :VLR-dwg-Reactor))
(VLR-dwg-Reactor
nil
'(VLR-beginSave . MCE3D))
)
)

 

From the help file:
A callback function is a regular AutoLISP function, which you define using
defun. However, there are some restrictions on what you can do in a callback
function. You cannot call AutoCAD commands using the command function. Also,
to access drawing objects, you must use ActiveX functions; entget and entmod
are not allowed inside callback functions. See Reactor Use Guidelines for
more information

 

Look at the docs for reactors.
If I'm not mistaken, the "Command" function is not allowed in reactor
callbacks.

file by using the vlr-dwg-reactor. Then I get an error message "Invalid
AutoCAD command". I am getting the same message if I try a regular AutoCAD
command. Like in the example below. Is it not possible to run commands when
using this reactor?