Cannot resolve the collation conflict between "SQL_Latin1_General_CP1_CI_AS" and "Latin1_General_CI_AS" in the equal to operation

I do the following:

...WHERE 
    fieldname COLLATE DATABASE_DEFAULT = otherfieldname COLLATE DATABASE_DEFAULT

Works every time. :)

You have a mismatch of two different collations in your table. You can check what collations each column in your table(s) has by using this query:

SELECT
    col.name, col.collation_name
FROM 
    sys.columns col
WHERE
    object_id = OBJECT_ID('YourTableName')

Collations are needed and used when ordering and comparing strings. It's generally a good idea to have a single, unique collation used throughout your database - don't use different collations within a single table or database - you're only asking for trouble....

Once you've settled for one single collation, you can change those tables / columns that don't match yet using this command:

ALTER TABLE YourTableName
  ALTER COLUMN OffendingColumn
    VARCHAR(100) COLLATE Latin1_General_CI_AS NOT NULL

Marc

UPDATE: to find the fulltext indices in your database, use this query here:

SELECT
    fti.object_Id,
    OBJECT_NAME(fti.object_id) 'Fulltext index',
    fti.is_enabled,
    i.name 'Index name',
    OBJECT_NAME(i.object_id) 'Table name'
FROM 
    sys.fulltext_indexes fti
INNER JOIN 
    sys.indexes i ON fti.unique_index_id = i.index_id

You can then drop the fulltext index using:

DROP FULLTEXT INDEX ON (tablename)

Use the collate clause in your query:

LEFT JOIN C tO_C on tA.FieldName = 'CID' AND tA.oldValue COLLATE Latin1_General_CI_AS = tO_C.Name  

I may not have the syntax exactly right (check BOL), but you can do this to change the collation on-the-fly for the query - you may need to add the clause for each join.

edit: I realized this was not quite right - the collate clause goes after the field you need to change - in this example I changed the collation on the tA.oldValue field.