Hello,
I've had this issue a few days ago — the symptoms are the same, at the very least.
Look into ~/Library/Application Support/Planeshift
Those are your settings, guild notes, chat history, etc.
Try to troubleshoot the issue by renaming the Planeshift directory in order to make Planeshift create a fresh one while keeping the old one.
Start the client, then quit, and in the newly created directory, add your old files (from the renamed directory) one at a time to find out which one is causing the problem.
My issue was resolved by removing the chat history file (well, I kept a copy; just moved the file elsewhere), it's in the logs subdirectory.