This usually indicates an error in code, because your memory limit of 320MB is not reached. If you look closely, the error occurred after only 20KBs where allocated.
If you're using K2 v2.9.0 or the dev version, then it's definitely not a K2 compatibility issue with PHP or Joomla. My guess is that some 3rd party plugin is to blame here. Look for any K2 specific third party plugins.
Fotis / JoomlaWorks Support Team
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