Hi Bob,
Fred has answered your question; however, if you wish to send an attachment in the future, you will need to use one of the following file types... bmp, txt, jpg, jpeg, gif, mpg, png, xls, xlsx.
You were probably trying to attach a PDF file, which is no longer allowed. You can convert the PDF file to one of the allowed file types and attach said file, or you can upload your PDF file to your online storage account and subsequently share the link to the file when commenting.