NullReferenceException at "Creating player" stage of loading any world/commecting to server

It looks like you have some old data,  and there is a need to clean it up.

Be careful,  because doing this will delete all your save data as well.

Backup any games you wish to save from Appdata and put them somewhere else, like on your desktop. 

 

After backing up any important save games : 

1. Navigate to your main game installation folder
2. Open the launcher executable
3. Click Tools, Clean game data, make sure ALL of the boxes are checked as in this picture:

 

Here is a video if you prefer a visual walkthrough (it does cover a bit more).

 

After that, verify the file integrity TWICE through Steam to ensure it catches any invalid files (sometimes it doesn't do it right on the first try). Three times to be sure.