Thank you for reaching us out.
Could you please add the NewtonSoft.Json.dll into GAC. Please use the dll which is deployed with the Testing Framework installation - it could be found in the bin folder. The default installation path is C:\Program Files (x86)\Telerik\Test Studio\Bin
if you have upgraded the product and C:\Program Files (x86)\Progress\Test Studio\Bin
if you have performed a new installation.
You could double check the version of the dll in the bin folder and if it is the same as the one listed in the exception.
I hope this will work for you as well. Though in case of questions please let me know!