Problem using .NET object in NAV

Hello,

I try to use a .NET object in NAV but have a problem. With simple code, it works : I can instantiate a object, and call a method which gives back the string I gave to the constructor. But now I have a program in C# which communicates with MS Project. When I tried with a code that only connects and gives back the projects' list in a string I obtain an error message (see screenshots below). The program works when I use it in a .NET program.

I think it is caused by the genericity used by the Load<> method. Is it right ?

Has someone any idea of a solution ?

Thanks