I just double checked the directory and file permissions. They are all set as the installation documents states.
I also found out that I can edit a post when logged in as the administrator but not when logged in as a regular user.
Then you need to check the permission of the
user group in the ubb control panel.
Control Panel » Group Management » Forum Permissions
Double check the:
Edit post time limit
This is a setting in minutes and specifies how long a post can be edited after it was initially created.
You will net to set the value to each forum by each group.
But the previous post suggests you may still have a chmod permission issue.