Multiple Problems

Gurus,
I recently started working with Apache POI framework to generate / update existing excel (.xlsx) report files. I am good with one report though...

But I am getting into issues while working on second report.
1. I am getting Formula evaluation exception while evaluating some formulas in sheet (especially where they are referring the data from other sheets - this workbook has multiple sheet)

2. One sheet (1) has chart / graph (manually created) using other sheet(2) data, after I create a new row in sheet 2, the chart is wiped out from sheet 1.

Can someone please help in this. Your help is much appreciated.

Thanks in advance,
YA