The line responsible to collect the selected lines is line 44 in main.py:

Qt Code: 
  1. updVars["SelectedColumns"] = self.ui.tbl_OpenFile.selectedItems()
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This is of course inside the function openFile(). This line instructs the program to update the global dictionary {updVars} in its element "SelectedColumns" (which is a Python list) with any - if any - selected columns of the table tbl_OpenFile. At least, that was my intention.

The problem is that after some tests* I have conducted, it is proved that the global dictionary is not updated and the element list "SelectedColumns" is empty, that's why the program ends with this error.

So, either the columns are not actually selected with a simple mouse click, or the code is not written that way.

Thomas.

*test: after instructing the program to return the length of the global list "SelectedItems", it returns 0, no matter what column selection has been done on the table.