Created Unassigned: v4.1 - We found a problem with some content [15577]

Hi,

I am getting that error message using the latest version 4.1 - works find on 4.0.5 but I need some of the new
features on the latest version like InsertColumn which copies comments, and notes etc...

error message
"We found a problem with some content in " when opening the file, after its stream as file.

This occurs when using GetAsByteArray()

I seen some examples like

Response.Clear();
Response.ClearHeaders();
Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
Response.AppendHeader("Content-Disposition", string.Format("attachment;filename={0}", fileName));
Response.BinaryWrite(output);
Response.Flush();
Response.End();

and

const string contentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
return File(output, contentType, fileName);

but neither is working .