I suspect this to be an issue with the file path. Microsoft Office imposes a 215 character limit on Office files. The quickest way to confirm this is to move 'DesignWorkbook_Stringinverter_Starkson.xlsx' to an uppper level folder than where it is and then try to open it. If it works then we can confirm it is the number of chracters in the folder path which is causing this issue. If the file still errors out, then I suggest you connect with our support team at firstname.lastname@example.org.
I hope this helps.
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