Object reference is not set to an instance of an object

I am getting an error message as : System.NullReferenceException: Object reference not set to an instance of an object.
And a message pops up to restart UIPath for every single time I add a new activity. Could anyone help me with this?

Internal_Error

This error occurs when u use any variable or argument which does not contains any value

Most likely your workflow file is broken.
1/ Try creating a new empty project to confirm the above assumption.
2/ Restore previous version of your project.

Cheers