Table cells not editable in Contribute

I have a date table (inside a CSS layout) which displays incorrectly in Contribute Edit mode.This is the URL http://www.greencs.co.uk/accreditations.html

In Contribute Edit mode, the right hand column of the table (which contains the PDF certificates) is pushed far out to the right (beyond the rest of the layout) which makes it impossible for the cells in this column to be edited. This also happens in Dreamweaver; the table width is 598 pixels but the Display width (in parenthesis in Dreamweaver) is 1300 px. Does anyone know why the Display width, which I assume Contribute is using in Edit mode, is so wide..... and how I can constrain it.

I have tried adding various table cell widths but to no avail. Help.....

Many thanks