If you see error message 'PHP Fatal error: Cannot redeclare function' or similar error message in your script, it means there is a problem with your script code (it tries to declare the same function multiple times).
This error says that your function is already defined. This could mean:
you have the same function defined in two files
you have the same function defined in two places in the same file
the file in which your function is defined is included two times (so, it seems the function is defined two times)