The problem is that you're using old outer join syntax. You just need to change it as it's no longer supported.

SELECT a.assignee,

sort = isnull(b.last_asgmnt, '0000-00-00.00:00:00') + a.assignee,

email,

phone,

pager

FROM assignee a

LEFT JOIN VW_LAST_ASGNMNT b ON a.assignee = b.assignee

WHERE a.assignee LIKE '$AUTO%' --As long as your collation is case insensitive.

AND a.available LIKE 'Y%'

AND groupname = @groupname

ORDER BY sort

Additional to this problem, I feel the need to advice you that this trigger will fail (silently) with multiple rows operations and will create some performance problems. I don't have enough information to indicate a better option and I'm sure this isn't the only problem that you'll have.

EDIT: I changed the code to remove the functions in your WHERE clause to allow them to use indexes if available.