Fatal error: Out of memory

I have a number of my sites set up as multi install sites using the mu plugin.

After the install things went well for 2-3 weeks. Now all I get is this stupid and frustrating error. I can access the front end, but cannot log in. I have confirmed the memory_limit is set to 64M so it can’t be that.

The failures occur in varied files – right now user.php on line 121 which is:

function wp_authenticate_cookie($user, $username, $password) {

But, a little while ago, it was something else and actually referred to a blank line!

I normally use Joomla, but have been forced to using WP and this sort of bug (which I have read, literally, 100s of posts for) amazes me.

I hope someone has an answer different to adding memory lines to htaccess, php.info (which I don’t have access to) or wp-config.php.

For an extreme measure I will just delete the multi site set up and reload all the sites, as I have 2 not on MU that usually work OK. Though they occasionally throw this error too.