That error means PostgreSQL (the program where PokerTracker 4 stores your poker data) isn't running. Have you done something recently to PostgreSQL like maybe deleting the "postgres" user from your Mac login screen? Has your computer shut down unexpectedly recently? Do you see PostgreSQL in your Applications folder? Please do this:
1. Confirm where your PostgreSQL is, probably here:
/Library/PostgreSQL/x.y
"x.y" will be two numbers such as "8.4", "9.0", etc.
2. Open a terminal, probably in "Utilities". In the terminal window copy/paste this:
sudo rm /Library/PostgreSQL/x.y/data/postmaster.pid
Substitute the "x.y" in that command with the numbers you noted in #1.
You want to delete "postmaster.pid" so answer "y" if the command finds it.
3. Next restart your computer and press/hold the "Alt/Option" key while starting PokerTracker 4 to enable logging.
4. If PokerTracker 4 still doesn't start please attach these files to a
Support Ticket:
--> /Users/{Mac Login}/Library/Application Support/PokerTracker 4/PokerTracker4.log
--> Your newest 3 or 4 PostgreSQL log files (look for "Mac" in the guide):
Guide: PostgreSQL log files