There's not enough information to help you really. What does your log file say? What exactly does "I cannot access JIRA" mean? i.e. what are you seeing?
What did you do to create this problem? Just try to log in? When did it start happening? Have you tried restarting JIRA?
For what it's worth, I have seen a similar message thrown by a plugin, and disabling it fixed it, but I can't remember which one it was and it could be a complete red-herring.
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