Your code does the following.
1) find a worksheet in the workbook
2) add that worksheet into the same workbook without changing the name
The result is that it finds that a worksheet already exists in the workbook with that name.
You need to give it a new name when you make the copy.
You would need to do "ws.CopyTo(wb,"NewName");
or "ws.CopyTo("NewName");
Check out the documentation https://closedxml.codeplex.com/wikipage?title=Copying%20Worksheets
1) find a worksheet in the workbook
2) add that worksheet into the same workbook without changing the name
The result is that it finds that a worksheet already exists in the workbook with that name.
You need to give it a new name when you make the copy.
You would need to do "ws.CopyTo(wb,"NewName");
or "ws.CopyTo("NewName");
Check out the documentation https://closedxml.codeplex.com/wikipage?title=Copying%20Worksheets