Index in position 2 exceeds array bounds in GUI

I am programming a GUI.

When I want to select only one column or first three columns of an outlined matrix from previous callback step (or in the related function), I encounter an error as "Index in position 2 exceeds array bounds", while I am sure that the matrix has more than one column and when I run that outside of the GUI, it works properly.

I dont know what should I do about this issue. Please guide me by an example.

Thank you in advance

[Alex Mcaulley]

Hint: Put a breakpoint in the line that is causing the error and see what is happening with the matrix...

[Jan]

Without seeing the code, having the data and the complete error message, Alex's suggestion is the only useful hint which can be given.