Comments by Member 2053006 (Top 3 by date)

Have you tried removing the GROUP BY section? My SQL is a bit rusty I am afraid, but it looks like that section is not needed and could cause problems.

Do NumeComplet and ClientId looking correct if you try enumerating the DataTable?

From the code you posted you are declaring the delegate reference as a static, so you can only reference one delegate, but you create a delegate instance for every WrapperClass instance.

If you create more then one WrapperClass then one of the delegate instances will go out of scope and cause this error.

Either remove the static in the first line to have a delegate reference for each WrapperClass or create a single delegate instance in the WapperClass static constructor (the callback function -UserResultFuc- should be passed the WrapperClass instance as a parameter)

One other thing to remember is you will need to remove the delegate when you are finished with the WrapperClass instance. A dispose method would probably be the best way to do this.