Simple:Press fatal error during install

I'm attempting to install Simple:stuck_out_tongue:ress in a brand new WPMU installation with goal of using Pro-sites, but I keep getting the following fatal error during activation of the SP plugin:

"Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to
allocate 72 bytes) in /home/hearye/public_html/wp-includes/functions.php on
line 3847"

Here's what I've tried to date but to no avail:

-- Confirmed my WP installation meets SP's minimum specs.
-- Confirmed I have ample memory.
-- I have tried the activation with all plugins turned off.
-- I have tried activating the plug-in network-wide and via my single-site.
-- Confirmed my WP installation is up-to-date.
-- Confirmed that SP is being used by others MU users without any (serious) problems.

Any ideas?