the strtotime() function uses the date separator as an indictation of the date format.
if the slash (/) separator is used, strtotime() assumes a US formated date:
if the dot (.) seperator is used, strtotime() assumes a UK formated date:
You datepicker was using the UK format with a slash as the separator which caused strtotime to be unable to recognize a valid date.
to fix your problem, I used str_replace to replace the / with . in the date at line 1:
if(isset($_POST['albumDate'])) $_POST['albumDate'] = str_replace("/",".",$_POST['albumDate']);
this passed the correct separator so the strtotime() function could read the date properly