Depending on which UPD release you find (mostly from Russian modding forums or Nexus Mods), the contents vary. A typical includes:
Here is a review of the film and its various iterations.
The most shocking comes in the first 20 minutes. The film asks: What if the timeline changed before Kyle Reese even traveled back?
The you are seeing is a Hard Stop Feature . It prevents gameplay until the software is synchronized with the developer's current server configuration.