Can't override a block template inside a panel pane

Hi I have a custom module that generates a block. I have assigned the block inside a panel pane and i'm trying to override the template of the block but it's not working.

My block delta is: expenses-chart

The template file i use is: panels-pane--block--charts-expenses-chart.tpl.php

I would really appreciate any hints.. Because this sounds like a major problem

Regards,