PHP Website fix

Hi, My server recently went down and its caused a few problems on my website when someone logs in and then clicks a link it automatically logs them back out. And when they try to join the website it comes up with an error. No one touched the code but when the server crashed and was rebooted those errors have occured on wow%fre%[login to view URL] (remove percentages). Please can you fix these. Thanks a lot Best Regards, Matt Lovett