Members cannot edit!

For several days now, my members have been unable to edit their posts. I have tried all things I can think of to fix this. I have confirmed that they have permission to do so. I, as administrator, can edit but members are reporting that they can only edit if they try to do it immediately after making their post. Once they wait a moment or two (or leave that section of the forum and go back to their post), they cannot edit. Some members are reporting that after a few moments, the Edit graphic completely disappears. Others are getting a message saying they can't edit. When I log in as a regular user, I'm having the issue of the button disappearing.

Please help!!

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Post edit duration limit for a member :Check None.

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See if that helps.