As discussed in the Mizner Law Firm Sovereign Immunity post, which you can access here, the Commonwealth of Pennsylvania generally cannot be sued for negligence or other types of torts which it or its employees cause.
Suing the King - Sovereign Immunity and its Exceptions
In old England, while the system of law we still use today was being developed, kings realized that the courts they were setting up might leave them vulnerable to being sued by their own subjects. In response, the principle of sovereign immunity was developed and enshrined as law: you cannot sue the king.