is the code above exact copy?
if so then inside most outer double quotes all other double quotes must be escaped with \
like so
$BigLink['active'] = "<a href='#NextLink#'><img id=\"thepic\" onClick=\"scaleImg('thepic')\" onLoad=\"scaleImg('thepic')\" src='#BigPhoto#' width='#Width#' height='#Height#' border='0' alt='Click here for next image'></a>";
$BigLink['notactive'] = "<img id=\"thepic\" onClick=\"scaleImg('thepic')\" onLoad=\"scaleImg('thepic')\" src='#BigPhoto#' width='#Width#' height='#Height#'>";