Can't Export Excel 2007 ?

Hello,
Since a moment, I can't export in excel 2007

I've got this error in the file :

Allowed memory size of 33554432 bytes exhausted (tried to allocate 311296 bytes) in <b>/var/www/vhosts/dddddd.com/httpdocs/salon62/plugins/PHPExcel/Writer/Excel2007/Theme.php</b>; on line <b>572</b><br />

What can I do ?
Thanks
Olivier

Lille (FRANCE)