1) You should have updated the field to:
<textarea id="Category_Description" name="Category_Description" tabindex="5" title="Please enter a value." ><?php echo((isset($_GET["invalid"])?ValidatedField("categoryupdate","Category_Description"):"".$row_WADAcategory["Category_Description"]."")); ?></textarea >
2) Line 84 also has an issue... it should be:
$WA_fieldValuesStr = "".((isset($_POST["Category"]))?$_POST["Category"]:"") ."" . $WA_AB_Split . "".((isset($_POST["Category_Code"]))?$_POST["Category_Code"]:"") ."" . $WA_AB_Split . "".((isset($_POST["Schofield_Stone"]))?$_POST["Schofield_Stone"]:"") ."" . $WA_AB_Split . "".((isset($_POST["Stone_Center"]))?$_POST["Stone_Center"]:"") ."" . $WA_AB_Split . "".((isset($_POST["3North"]))?$_POST["3North"]:"") ."" . $WA_AB_Split . "".((isset($_POST["Category_Description"]))?$_POST["Category_Description"]:"") ."";