Field assignment to a non-structure array object

Hello,

I have a block(Subsystem) in the simulink with a mask, if I double click this block, then an GUI with an edit box and button would appearing. The button is to choose the data in my computer and the edit box to show a List ( as a result from my code ). Then, if an element from this list chosen, a number should be shown in an other block(Block2)

set_param(XXX, 'bitpatterns', YYY).

It worked, however, just for the first attempt, and for the next attempt it says

 "Error evaluating 'MaskCallback' callback of Subsystem block(mask) 'main/Subsystem'. (btw. 'main' is the name of the file, main.slx)

Field assignment to a non-structure array object.

anyone have an idea?

[Sivakumaran Chandrasekaran]

share the screenshot of the error. so that it can help us to understand more.