Hi Sherry,
in Profile, under EFILE options, you enter your business number , a 15 digits number, and you create the XML (the XML will include this business number), then on the CRA website, you enter the exact same 15 digits business number and the WAC, associated with the business number. If this doe snot work, its might be that your WAC does not allow filing T5, you would need to request a WAC for T5.
Hope this helps.
