Fatal memory error



Hello,
I just got back from a three day trip and the back-end of the website I've been building doesn't work. It was working fine when I left and when I got home and tried to log in I get this message:

Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 48 bytes) in /data/19/1/77/113/1892602/user/2058644/htdocs/dev/includes/menu.inc on line 257

Then if I hit 'refresh' the message changes to:

Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 4104 bytes) in /data/19/1/77/113/1892602/user/2058644/htdocs/dev/includes/menu.inc on line 637

After that no matter how much I refresh the page I keep getting the 2nd message.
If I go to the menu.inc file in the /includes folder here is what is on line 257:
if ($data = unserialize($data)) {

And here is what is on line 637:
$item['options'] = unserialize($item['options']);

Neither one of these lines seem to have anything to do with memory size. :(

Now, the front side of the site seems to work but if I click login and put in my credentials I get the above messages.

I'm very new to drupal and I'm really more of a pc break/fix tech than a web developer. Would someone please tell me how to correct this so I can get back into the back-end of my site?
And I'm curious as to how this happened. All was fine when I left.

Solution: Increase memory_limit to 64M or 128M in php.ini.