Hi Essam Saed ,
This warning message:
warning MSB3270: There was a mismatch between the processor architecture of the project being built "MSIL" and the processor architecture of the reference "C:\Users\essam\source\repos\Lean\Research\bin\Debug\QuantConnect.Research.dll", "AMD64". This mismatch may cause runtime failures. Please consider changing the targeted processor architecture of your project through the Configuration Manager so as to align the processor architectures between your project and references, or take a dependency on references with a processor architecture that matches the targeted processor architecture of your project.
gives us a hint that you might be compiling Lean with the wrong processor architecture. That's why I asked you to get the latest version since a similar issue was solved by #4593...
Do you know which Lean version had worked on your computer? The Net Framework upgrade can be the cause, but it was merged mid-May. However, it's likely an issue with your system, and probably you will have to do a major clean up (remove and reinstall Net Framework, Visual Studio, etc).