If you want faster help, provide more details instead of just bumping the thread. It may be 1000 different issues looking at your current description. Not to mention that you should have opened your own thread... Please look at the error log and provide anything we can work with.
Also, the solution provided by DiegoPino should most likely work. So "I think this for me will not work" doesn't help you either.. If someone gives you a solution, test it, you have nothing to lose, except 3 minutes of life spent to download MyBB 1.8.5, switch the mentioned files and switch them back to 1.8.6 if that doesn't help.
Also, the solution provided by DiegoPino should most likely work. So "I think this for me will not work" doesn't help you either.. If someone gives you a solution, test it, you have nothing to lose, except 3 minutes of life spent to download MyBB 1.8.5, switch the mentioned files and switch them back to 1.8.6 if that doesn't help.