expanding on Riider's reply, at the bottom of the list of folders (inbox/sent etc.) on the left of the yahoo screen there are some optional applications.
One 'Attach Large Files' relates to files upto 2gb in size. This may help if the file exceeds the 25mb limit.
However, am puzzled by the Norton Antivirus reference. This suggests yahoo does not 'like' the file due to a possible virus or similar, and wants it removed before allowing attachment.
Please advise back on progress.
Good Luck - Keep us posted.