It is possible that the option was turned off in the system.xml file. The file is located at cognos/c83/templates/ps/portal.
It would be under <param ui=hide>
<CC_RUN_OPTIONS_email_attachment/>
</param>
just remove it, save the file, and restart the cognos services.
BUT - it might have been turned off for performance reasons. AND:
make a backup of the system.xml file before doing any work, and the file is easily corrupted, so use notepad or a very basic text editor to work with it as xml editors add values to the files that invisible in standard editing, but cause the file to work improperly.