Can someone please assist with this problem, I am running the Nxt wallet (shows version 2.2.0 at the top) on a Mac running OSX El Capitan version 10.11.1 (15B42). The wallet has been running perfectly for a long time and I shut it down to reboot the machine and now the Nxt wallet will not start again, when it starts up it goes through some checks and then displays the following error message:

It then comes to the last screen like:

Where it stays for hours and never opens the welcome screen and the wallet, so what can I do please?
I have tried a few times and it either freezes before the last screen or it freezes at the last screen.