Runtime error 1004 when trying to save file via VBA

Hello,

I'm trying to save a file to a specified folder with a custom filename depending on the contents of certain cells.

Everything used to work fine, however suddenly I got Runtime error 1004: the specified dimension is not valid for the current chart type whenever the macro gets to the save-routine.

Code looks as follows:

To generate the filename:

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And then to save the file:

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The code chokes at ActiveWorkbook.SaveAs fileSaveName, FileFormat:=xlOpenXMLWorkbookMacroEnabled.

Does anyone have any idea what may cause this problem? Note that a chart appears in the worksheet, but I don't refer to it anywhere in the code...

Thanks; I'm aware of that trick.

However I would like to know what causes this error rather than ignoring it...