Input field array ends up as "Array" string

Hi every body. I have a form that was originally working just fine. It had a series of input checkboxes with the same name ("interests[]"). These values then ended up in an array ($_POST['interests']), which I then imploded into a comma separated list ($interests = implode(', ', $_POST['interests']); ). Well, that was working just fine until yesterday when I started getting an error on that implode function ("Bad arguments to implode()"). So I did a "gettype" on $_POST['interests'] and it revealed that it is now ending up as a "string" variable. So I printed it and it contains the string "Array"! Anyone know what's going on here? Thanks --Dan