Your problem is the trailing slash you have on your opening <cfexchangecontact> tag:
<cfexchangecontact ... />
That looks to the CF server as if you're trying to do:
<cfexchangecontact ...></cfexchangecontact>
When you're really trying to do:
<cfexchangecontact>
<cfexchangefilter>
</cfexchangecontact>
Simply remove that / so it looks like:
<cfexchangecontact action="get"
name="qContacts" username="#mailuser#"
password = "#mailuserpassword#"
mailboxname="#mailboxname#"
server="#mailserver#">
<cfexchangefilter name="maxRows" value="-1">
</cfexchangecontact>