The collation must exactly match on a join or the query will fail if both fields have a defined
There are lots of absolutely identical collations (for example the default UK and US settings are identical yet incompatible).
There is no easy way of correcting the databases collation other than using DTS to completely copy the database.
The following is the solution to all collation blues:
This needs to be after the appropriate join :
where bar1 = bar2
This eliminates the problem.