Table border issue

Question

I have a table in xsls(Same as Html). Inside this table, I have another table. I set the border of both tables to "0". Cellpadding and Cellspacing for both tables are "1" . The problem I m facing is that, the first cell of inner table makes a thicker upper border, which i guess because of the combination of outer table's cell's bottom border and top border of inner table's cell. I have tried much to remove this thick line, but no luck ... !!!

Any kind of help will be highly appreciated ..