You need to use the same collation for both sides of your comparison.

In your situation, one server ignores accent marks when comparing, the other includes accent marks in the comparison.

If one server is set to 'HELENA' = 'HÉLÈNA' and the other is set to 'HELENA' <> 'HÉLÈNA', when you cross server boundaries using different collations with 'HELENA' = 'HÉLÈNA', the server doesn't know how to answer the question.

Set one side of your comparison to match the collation of the other.

http://msdn.microsoft.com/en-us/library/ms184391.aspx