Report.ExportToImage() triggers error

Hi, im trying to export 2DAxis to a png file, but i error, the code is simple like this and the report object exists and has one curve

Report.Settings.ImageExport.PNG.BitsPerPixel = ePNGBitsPerPixelRGB24
Report.Settings.ImageExport.PNG.Width = 300
Report.Settings.ImageExport.PNG.UseRatio = True
Call report.ActiveSheet.Objects("2DAxis1").ExportToImage("C:\DEV\axis", eImageExportTypePNG)

I tried it like this without file extension specified like is written in help, and as well with extension. still the same error:

Diadem 2017 64bit, windows 7