error message while trying to load dashboard

Fatal error: Allowed memory size of 262144 bytes exhausted (tried to allocate 4864 bytes) in /home/*******/public_html/alaskaphotos/wp-includes/load.php on line 381

I have several identical sites that work fine, even copied the includes folder from a working site to no avail. Increased memory fro 256 to 320k in default constants file.