Ok...
First of all I was using the CslaGen version from 2007.
After downloading the new version from 2009, I thought the error would
go away BUT it didn't. So I used the database publishing wizard,
republished my database schema and created a new database exactly like
the other one.
And then, by miracle, the error was gone.
I figure out this must have something to do with some nasty piece of
code the T4 Toolbox is inserting and it is conflicting with the
CslaGen. Who knows...
Thanks guys,