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I just tried something and it has fixed it.
I removed the config file, restarted and it replaced config with new one and didn't crash.
So clearly something has broke something somewhere!!
No idea why where or what.
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I have started to see this error.
As far as I know I haven't done anything other than changed some settings in my config file.
I replaced the exe file with the 1.7 version offered in the downloads section here.
Any help?