Error loading 'ThomsonReuters.Udap.BusTools.DLL' assembly.

Could I ask you what you are trying to do?

Is it an ASP .NET project?

Most likely you're missing one of the dependencies of ThomsonReuters.Udap.BusTools.dll in your build folder. Here's the list of the files you need to have in the build folder:
Common.Logging.dll
EikonPipeDll.dll
i18nresource.dll
protobuf-net.dll
Newtonsoft.Json.dll
ThomsonReuters.Desktop.SDK.DataAccess.dll
ThomsonReuters.Udap.BusTools.dll
ThomsonReuters.Udap.Ipc.Managed.Common.dll
ThomsonReuters.Udap.ManagedPS.dll
You may also need Microsoft C Runtime libraries (msvcp120.dll and msvcr120.dll) in the build folder if they're not found in the PATH.
Please also be advised that the data usage rights that come with Eikon only permit the usage of data retrieved from Eikon "for the user's individual use". If you're using data retrieved from Eikon in a Web server application, and you're only licensed for Eikon, you may be in violation of your contract with Thomson Reuters.

Couple more sanity checks:
1. Can you tell me the version of Eikon .NET SDK you downloaded from NuGet? Best if you just attach your packages.config file here.
2. You're trying to run this application on a machine where Eikon is installed, right?

The list of packages looks good. Clearly there's something missing, but I'm out of ideas of what it might be. Try creating a new project, installing Eikon 4 Desktop Data APIs into it, compiling and running it.