Estimate Weightage not updating

Dear All,

can anybody please address this issue...

I had to assign the est weights to all the activites so i exported the project with all the activites along with the est weight column.I assigned the est weights to all the activities as required and imported back to the same project.But for my surprise the est weights was not changed as i had done.it is still shwoing as 1.0  for all the activites.

Why was the est weights updation was not successful..

please reply back to this strange thing..

thanks in advance..