@isra sahli - when you set a new field in the handles structure, you need to save the change to that structure so that the updated structure is available to other callbacks. You need to add a line of code as follows:
function choose_tissue_file_Callback(hObject, eventdata, handles)
[tissuefilename pathname] = uigetfile({'*.mci'},'File Selector')
handles.tissue_file_name=tissuefilename
guidata(hObject, handles); % <----- need this line
function choose_illcol_setup_Callback(hObject, eventdata, handles)
[illcolsetupfilename pathname] = uigetfile({'*.txt'},'File Selector')
handles.illcolsetup_file_name=illcolsetupfilename
guidata(hObject, handles); % <----- need this line
Note that if you don't add this line, then the field won't be present in the structure and so you will see the above error about the non-existent field.
