Observed the same symptoms as described (see picture of neverending Add Attachments). I did not mingle with any settings, nor un-installed SilverLight, I simply found that my attachments had valid filenames (in Win7) but apparently not valid when trying to attach them with (Chrome in my case) ! I found the tip here in this useful ressource here (near end): [http://help.yahoo.com/l/ca/rogers/mail/classic/technical/browser-11.html Yahoo Mail Roger's issue] I renamed my file, retried, and voila - it took less than 10 sec to Virus check my 50K Excel file. Hope it helps.. P.S. Now - why doesn't the script check filenaming limitation, before attempting to pull them inside the mail ?