Colation Problem

Hi,
I am using SQLServer 2000 with SP4 and I am getting a strange collation problem.
I have three tables, TEmployee, TMechanic and TManager, each with the two columns Firstname, Lastname which are both varchars.

I run the following query:
<PRE>
SELECT OUTERUNION.FIRSTNAME, OUTERUNION.LASTNAME FROM ((
SELECT QUERY1.FIRSTNAME, QUERY1.LASTNAME
FROM
TEmployee query1 WHERE FIRSTNAME = 'John'
UNION ALL
SELECT QUERY1.FIRSTNAME, QUERY1.LASTNAME
FROM
TCoManager query1 WHERE FIRSTNAME = 'John'
UNION ALL
SELECT QUERY1.FIRSTNAME, QUERY1.LASTNAME
FROM TMechanic query1 WHERE FIRSTNAME = 'John')
UNION
(SELECT QUERY2.FIRSTNAME, QUERY2.LASTNAME
FROM TEmployee query2 WHERE FIRSTNAME = 'Michael'
UNION ALL
SELECT QUERY2.FIRSTNAME, QUERY2.LASTNAME
FROM
TCoManager query2 WHERE FIRSTNAME = 'Michael'
UNION ALL
SELECT QUERY2.FIRSTNAME, QUERY2.LASTNAME FROM TMechanic query2 WHERE FIRSTNAME = 'Michael'
)) OUTERUNION

</PRE>

I get the following error:
Cannot resolve collation conflict for column 2 in SELECT statement.

If I change my select statement to only have one column (doesn't matter which column) it doesn't happen.

Any ideas, greatly appreciated?