Found some interesting statements here:

https://technet.microsoft.com/en-us/library/ms178086(v=sql.105).aspx

Have to wonder if there might not be a DENY in place somewhere with respect to SHOWPLAN permissions, such that anything less than a reversal of the DENY would allow...

Try this on for size:DECLARE @startdate AS datetime = '01 Oct 2017',
        @enddate AS datetime = '02 Oct 2017';

SELECT DISTINCT
    co.BTEmail AS Email,
    co.BTFirstName AS FirstName,
    co.BTLastName AS...

I noticed that your query does not identify the data type of the @Grouping variable.  You are testing it for equality with a character string, so if it's a bit...

Try this on for size:
DECLARE @table AS TABLE (
    ID int,
    empnum int,
    email varchar(100),
    fName varchar(100),
    lName varchar(100)
);
INSERT @table (ID, empnum, email, fName, lName)
    VALUES    (1, 123,...