We have a small application used by a few users that has been running fine for almost a year. One of the users who has been using this on a daily basis started getting "500 Internal Server Error" right after entering credentials. I tried enabling debug info at level 5 first and then 8 and then 9 but I am not seeing any issues. All the logs show successful login and rending of the page. No other users are having this problem. Authentication and authorization are all passing fine. I even had her use my computer but getting the same error. Any ideas how to trouble shoot this?