Readable error message for overwriting analysis figures that are already open
Description
Today I tried to run an re-run an analysis I had already done before, but I still had the png file for one of the figures open on my computer (which was generated a previous time the analysis code was run). This caused an error when the analysis code tried to overwrite the figure. Unfortunately this is not a very readable error, and may confuse users
I suggest changing this error message to something that indicates that the open png file is the cause of the problem.
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