New Post: getValue returns null on specific sheet

What type of formating can prevent PHPExcel from reading dato from a cell?

I'm using the string

    $cellContent = $objPHPExcel->getActiveSheet()->getCell($cellID)->getValue();
    var_dump ($cellContent);

The var_dump returns null when $cellID has certain values even though I now the cell holds a string.

The cells are merged but I have reconstructed the sheet and there i have no trouble at all reading the exact same merged cells.

The production sheet is locked for editing but I don't think that it should give any trouble as I can read other cells in the sheet.