Your LimeSurvey version: LimeSurvey Community Edition Version 6.4.0+231218 
Own server or LimeSurvey hosting: own server
Survey theme/template:
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I am trying to use the import survey function. From the 'Create, import, or copy survey' screen when I select Import and choose a .TXT file I receive the following error: 500: Internal Server Error array_map(): Argument #2 ($array) must be of type array, bool given

Details

• The file was created by exporting an existing survey
• The file imports without error if not modified
• If I open the file in Excel as a tab separated values file with headers and click save without making any changes, I receive the error.

Excel is often causing problems.

Try to work with Libreoffice Calc and see what happens.