If you see PHP Fatal error: Cannot redeclare function it means that there is a problem in your code (it tries to declare the same function several times). We do not provide coding services, you can find the problem on specialized resources, for example:
http://www.google.com/search?q=PHP+Fatal+error+Cannot+redeclare
This error means 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 that the function is defined two times)
To help with the third point, the solution would be to use include_once instead of include when including your functions.php file, so it cannot be included more than once.