If you have an embedded API test as step, which has a code behind file, you might encounter similar error after updating Test Studio:
Could not load file or assembly 'Telerik.ApiTesting.Framework, Version=xxxx.x.xxx.xxxx, Culture=neutral, PublicKeyToken=xxx' or one of its dependencies. The system cannot find the file specified.
This means that the API embeded project was built with the previous version of APITesting Framework and the dll files were generated with that version.
To fix this error, you need to rebuild the project with the latest installed version of the framework. To do that, delete the mentioned assembly files in the bin folder of the embedded API project. It is located in the ApiTests subfolder under the project root folder, like C:\MyTestStudioProject\ApiTests\bin. That way the API project will be rebuilt with the new Telerik.APITesting.Framwork assembly and resolve the error occurance.