..and judging from the files and lines mentioned, it looks like it's because you're including functions.php() twice.
If functions.php only contains function definitions, try using include_once() to include it, instead.
"That seemed like a rash assumption," he murmered, disapprovingly.
"Ah ha," I said, pleased to have caught him out for once. "That's why I said If it only contains definitions! If it had main code it wouldn't work."
He sucked thoughtfully on a ballpoint pen. "Enunciate your words better. Put spaces between them." he slurred around its shaft.
