Some users with Internet Explorer (IE), versions 9 and higher, may have an issue attaching files to their secure messages.  In this case, there are a few options:

1) Temporarily enable 'InPrivate Browsing'.

Open Internet Explorer.  Then select 'Tools' > 'InPrivate Browsing'.  A new Internet Explorer window will open.  Using this new window, log into the Secure Message center and you will be able to add the desired attachment.

2) Alternatively, you can use one of the other supported browsers to attach your file.