Hello @larseline , you only included the .aimms file in your attachment. That doesn’t let us see what code is giving this error. Please attach the full project as detailed in 

https://how-to.aimms.com/Articles/45/45-share-project-files.html

Are you sure that, next to trying to save the Excel workbook using AIMMS, you do not have the workbook open in Excel itself at the same time? That would explain this error message, as Excel would then ‘lock’ the workbook.

Regards,

Mischa

Hi @larseline , wonder if @Mischa 's and/or @mohansx 's answers helped you? Thanks for sharing.

@Patrick @Mischa @mohansx  Sorry for the late reply.

Yes I still had the workbook open. So I had the option to close the workbook and open it afterwards again.

As I didn’t like that option I created an Excel supportfile and a VBA code now copies the data from the closed supportfile workbook to my working file.

Thank you for your support!