if you can not call from main programe , probably u r doing something at there whitch may delay, overlap or changing properties of your object. just try and see only calling your sub routine nothing else in main programe.
What language are you scripting in?
That may have an effect depending what you're passing in to get to the function that fails.
From here: http://support.smartbear.com/viewarticle/70308/
•JScript, C++Script and C#Script do not support functions that obtain parameters by reference
May have something to do with it?
And, as dmiscannon says, adding a sys,refresh just before trying to use the object may help.
