I have used the following code for several years and never had an issue down loading .docx file from our web site to the user.

Code:
                    Dim fi As New IO.FileInfo(FileName)
                    'Resp is a HttpResponse from DwnLD.aspx.vb
                    Resp.Clear()
                    Resp.ClearHeaders()
                    Resp.ClearContent()
                    Resp.AppendHeader("Content-Disposition", "attachment; filename=" & IO.Path.GetFileName(FileName))
                    Resp.AppendHeader("Content-Length", fi.Length.ToString())
                    'hmmm....
                    '                   "application/octet-stream"
                    'for .docx files
                    '                   "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
                    ' Resp.ContentType = "application/vnd.openxmlformats-officedocument.wordprocessing*?ml.document"
                    Resp.ContentType = System.Web.MimeMapping.GetMimeMapping(FileName)
                    Resp.TransmitFile(FileName)
                    Resp.Flush()
We recently updated the server and now users can't download the files. We get a file name and network error in the download files drop down. Don't have the error when running in the development environment.

Windows server version - 24H2
IIS Version - 10.0.26100.1

Checked the IIS log, no errors.

It was a full server replacement.

We checked the MIME type and .docx is there.

Any help is appreciated. THX