A: 

In your mapping, set the string property length to 4001 or higher:

Map(x => x.FirstName).Length(4001);
Jamie Ide
That is the exact mapping that is causing the problem.
berko
Show the mapping in the question next time and maybe you'll get a better answer. 4001 (or higher) is working for me in SQL 2005 (not express).
Jamie Ide
A: 

The solution is not really an answer.... but works anyway. To fix the issue I changed the length in the mapping to 10000. Now it all works.

So my mappings would now look like :

Map(x => x.FirstName).Length(10000);

Go figure.

It would be great is someone could shed some light on this peculiarity.

berko