session var puzzle

Dear list, I am sorry for the second posting, but this is going to drive me to drink something other than lattes! I have one page, index.php. when it calls mod_sub, a directory type of page is printed. Here I am trying to set a session var of the most recently selected category to allow the user to return the to same place in the directory. when I do this: $_SESSION['CategoryID'] = 230; in mod_sub then in mod_profile: print($_SESSION['CategoryID']); will print 230 when I do this: $Tmp = 230; $_SESSION['CategoryID'] = $Tmp; in mod_sub in mod_profile: print($_SESSION['CategoryID']); will print 230 BUT, when I do this: $_SESSION['CategoryID'] = $Data['ID']; in mod_sub $_SESSION['CategoryID'] = intval($Data['ID']); in mod_profile: print($_SESSION['CategoryID']); will print '' and 0 I am setting several other session variables throughout the code without any unexpected behavior. I have even tried changing the index to something odd in case I am resetting 'CategoryID' somewhere and forgotten it. But no matter what I try, once I set it "= $Data['ID']" I get the odd result. BTW, if I print $_SESSION['CategoryID'] from mod_sub right after setting, it holds the expected value. This is really frustrating, I must be missing something basic about the way session vars can be set. Kathleen