template/css problem

Hi,
I have made up a website using css and a template file. I have three columns the left and right column measurements in pixels and the centre expanding to fit the screen width. The problem I am having is with my template - I can edit my editable region (body copy on each page) in design view but not in code view. It comes up with the message:
'Making this change would require changing code that is locked by a template or a translator. The change will be discarded.'
The content I am trying to change though is in the editable region. I am wondering if this is related to my expanding css column? Can anyone help? Really appreciate it.
Thanks.