System.NotImplementedException error

The specific method you are calling (considering it is not a class library method) is more than likely specifically doing this:

 throw new NotImplementedException();

It's a stub right now. This is code in your solution; so on your page, your method is likely not implemented.

You or someone else might have added the GetPersonnel() method using Visual Studio auto code generation technique which inserts a NotImplementedException line in code and you have to manually remove it.

Inside your GetPersonnel() method, remove the throw new NotImplementedException... line, and implement the method completely to return some value matching the return type of the method.