>Seen like all the code is mixed. We compile this class as a dll on our web server. As soon we add a property (and we don't use this propertie in code, just adding that's all) the code fail in some method that was working properly. We receive error like data mismatch. If we remove the propertie but add a new one to make another test the code will fail in another method (not the same) with some error message.

Michel,

Did you re-register DLL on the web server after modification?