Undefined class constant

Hi everyone, I'm having a hard time dealing with an error that appeared overnight in one of my PHP script: Fatal error: Undefined class constant 'self::TYPE_HIDDEN' in /#########/classes/framework/HTML/HTMLForm.php on line 120 HTMLForm.php snippet: ......... // Creates the HTMLFormFields foreach ($this->Record->Columns as $_column) { // Add only visible columns if ($_column->IsVisible) { // Default field type $_type=HTMLFormField::ELEMENT_TYPE_TEXT ;

                // Adjust default type based on Column type
                switch ($_column->Type)
                {
                	case Column::TYPE_AUTONUMBER:                    			  $_type=HTMLFormField::ELEMENT_TYPE_HIDDEN ;
                          break;

case Column::TYPE_BOOLEAN :

                          $_type=HTMLFormField::ELEMENT_TYPE_CHECKBOX ;
                          break;
                        default:
                          break;
117:           }

118: 119: // Add the column to the list of fields 120: $this->Fields[$_column->Name]=new 121: HTMLFormField($this->Name,$_column,$_type); 122: 123: } } As you can see there is no refference to any TYPE_HIDDEN constant at line 120, nor in the HTMLFormField's constructor. I searched the net, but I just can't find the reason of this. Can someone please help me ? Thanks, Puiu