Watch.dogs.2.multi16.update.v1.17.part4.rar -

Ensure you aren't missing any .rar files in the sequence.

Watch Dogs 2 – 1.17 Patch Notes – Bug Fix Patch - Steam News Watch.Dogs.2.MULTi16.Update.v1.17.part4.rar

If the game won't launch, try running it in Windows 7/8 Compatibility Mode or as an Administrator via the application properties. Ensure you aren't missing any