I know these reports are old - the answer is for any reader finding this issue since then :)
It's a PHP memory issue
You need to increase memory limit
One way is in wp-config
http://codex.wordpress.org/Editing_wp-config.php#Increasing_memory_allocated_to_PHP
If this doesn't work, the you need to change it in php.ini (found in root folder for website).
NOTE: If you're using shared hosting you may need to ask your hosting company to do this.
Set it to 128MB, don't waste time with 98MB or whatever - 128MB should be enough for almost any WordPress site
