VFP 9 SP 1: Odd Run-time Error

The following line runs fine under a development system.  Under
the run-time, it throws error 1001 (Feature is not available.):
     browses.addproperty("filter1",chrtran(this.wfctlist," ",""),1)

     browses is an object of type basiccustom which is a subclass of
custom.  basiccustom simply adds a method called .dorelease() which is
equivalent to most classes .release().

     this.wfctlist is an input field four characters long.

     browses.filter1 does not already exist (though this should not
matter).

     The docs for .addproperty do not have anything about limitations
under the run-time (except for the fourth optional parameter which I
am not using).

     What am I missing here?

Sincerely,

Gene Wirchenko

Computerese Irregular Verb Conjugation:
     I have preferences.
     You have biases.
     He/She has prejudices.