Following error can occur, when creating an instance of a .net class in C/AL:

Reasons:

• If the assembly is used on client side (property RunOnClient=True), then the assembly was not copied to the local Add-ins Folder of the RTC Client. To copy the assembly into this folder you need in most cases Admin rights. So, check that first.
• If the assembly is used on server side (property RunOnClient=False), then there might be a version conflict between the assembly file located in the Add-ins Folder of the Nav Service and the used version in the C/AL Code. That can easy occur after installing Updates. So update the code and restart the nav service.
• Missing System permission: That means, that the assembly was copied from the web or from a computer outside the local network to a target computer/server with windows server OS. Then, the assembly is automatically blocked by the system.