Fatal error: Allowed Memory Size Exhausted

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 84 bytes) in /home/sitename/public_html/wp-includes/wp-db.php on line 178

Cause

This error means that your server has run out of memory while activating Feed to Post. 

The Feed to Post add-on:

• Imports items differently than the core WP RSS Aggregator plugin.
• Imports items differently than the Simple Feeds Bundle add-ons.
• Requires much more data to be collected about the items in the feed in order to convert them into posts in your system.

This is why when Feed to Post gets activated:

• it must delete any existing feed items imported without it.
• their format becomes obsolete and different to that of posts created by Feed to Post.

If you have a very large number of feed items imported before the activation of Feed to Post, chances are that you may run out of memory, because all these posts are stored in memory.

Solution

The best way to deal with this is to purge imported feed items, a feed source at a time, by clicking the Delete Posts link for every respective feed source and then wait until all feed items are deleted. 

You can do this a few feed sources at a time by opening the Delete Posts link in a new tab or window, especially if they don’t have a very large amount of feed items imported. 

Unfortunately, there is no way around this.