one of wp site give me memory error

I have a multisite installation, but only one site give me error, i have the wpml translate plug in and marketpress more compared to the other....
My isp says I have to do an upgrade to a hosting plan with more memory...is possible?

This is the error message
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 16384 bytes) in /home/gradimen/public_html/wp-includes/functions.php on line 4148

Thank you
Andrea