Fatal error: Cannot redeclare function_name() (previously declared in file.php:10) in file.php on line 10
A variation of this error message sometimes appears after installing hacks or making certain other edits to your forum's files. In order to perform the variety of tasks that go into managing and displaying a forum, each page must process code stored in several different files. When this error is displayed, it is an indication that some code is either being processed twice or shares a name with another area of code.
To determine which case you are dealing with, compare the two file names mentioned in the error message. These are shown in green and red text in the example. When the two filenames are identical, this indicates that the page is attempting to process the named file more than once. Look at Case 1 below for a solution. If the two filenames are different, two pieces of code are sharing a name; this is covered in Case 2.