PHPExcel中的函数

I've been using PHPExcel to both read and write to an Excel workbook. When I try to get the cacluated value of a cell with the getCalculatedValue method, it seems to quit on the page mid loading, but not return any exception before. When using the ACTUAL workbook, the cell is fine and working.

The actual function in the cell is:

=IF($B$8="Option 1",0,IF($B$29=H$47,'WorkSheet2'!$H$12,0))

Does anyone have any idea what could be causing the page load failure, without any exception thrown?

the problem code is in this line:

$cell->getCalculatedValue();