Hi Juan,
Below I am going to give several variations on a procedure to reproduce this error. Please be patient, the problem is intermittent. Sometimes it will take 10 or even 20 or more tries of this procedure to reproduce the problem.
I have attached a script for you to use. Also I have attached screen captures of the exceptions I have seen. The exceptions vary in their addresses. Also please locate the image NGC1808_L.fit from PI's video tutorial to use with this procedure.
1 - Reset PixInsight Settings.
2 - Open PixInsight.
3 - Open NGC1808_L.fit.
4 - Press Cntl-A to invoke the 'STF AutoStretch' command.
5 - In the Script Editor, open the attached script.
6 - In the Script Editor choose the 'Execute -> Compile & Run' command.
7 - Drag the Dialog's New Instance icon to the workspace.
8 - Click the Dialog's Ok button.
9 - Right click the script icon, choose the 'Delete Script Icon' command.
If no system exception occurs, close the mosaic window and repeat steps (6) through (9).
The system exception also occurs in variations of this procedure:
Variation 1: After dragging the New Instance icon to the desktop, click the Dialog's Cancel button and then delete the icon.
Variation 2: Don't open NGC1808_L.fit. Just run the script, drag the icon to the desktop, click Cancel and then delete the icon.
Multiple tries of these procedures will be necessary to see the exception. Sometimes exiting and reopening PixInsight helps to make the problem occur. It is very intermittent, please be patient.
Thanks,
Mike