The above error can occur for a number of reasons. If developing a Dynamics GP addin and you are attempting to run the addin as an application outside of GP, then this error may be encountered if anything from GP’s dexterity is requested by the code via the bridge dll.
The bridge dll is the route into GP for .NET addin development, but if something is requested from GP then the dexterity shared components dependencies are required to be on the environmental paths. When the addin is ran as an addin by the Dynamics GP process, the dependencies are provided by Dynamics GP, from the application folder. When running a free standing GP app, then these must be made available to the application through putting the dlls in the .net application’s folder. Putting TNTLIB.dll and DDAPI.dll would be expected to prevent further errors.