Error Running Contributions Summary Report
It seems like you have some invalid data in your database.  I don't think this is related to file permissions or caches.  Is it possible that you imported data via a SQL command rather than the UI or API?

Try turning on the backtrace function in Administer menu > CiviCRM > Debugging and Error Handling, and hopefully you'll get a better sense of which field this is supposed to be.  Alternatively, look at the fields that are likely to be called in your instance of the report - checking columns, filters, etc. - and then run SQL commands to find a datetime field with a value of "201401".

Since this is likely to be in civicrm_contribution, I looked up the datetime fields in that table.  There are four.  Try running these commands, then see how this data get entered?

SELECT id, contact_id, receive_date FROM civicrm_contribution WHERE receive_date = '201401';
SELECT id, contact_id, receipt_date FROM civicrm_contribution WHERE receipt_date = '201401';
SELECT id, contact_id, cancel_date FROM civicrm_contribution WHERE cancel_date = '201401';
SELECT id, contact_id, thankyou_date FROM civicrm_contribution WHERE thankyou_date = '201401';


UPDATE: That backtrace is super-helpful!  I looked at the code in CRM/Form/Contribute/Summary.php and I see better what's happening here. The issue is still invalid data - just not in the format I expected.

This part of the code is the part that creates the links on the Summary Report to drill-down links.  See the links in the screenshot:


So Civi is converting the start dates of each of those months into a different format.  One of your contributions still seems to be happening in a different month.


You can try commenting out lines 737-786 of the file I mentioned - you'll lose the drill-down links, but hopefully the invalid data doesn't affect anything else.
This bug shouldn't trigger unless you're grouping by receive date.
You can try tracking down that bad data.  Try this SQL:

SELECT id, contact_id, receive_date FROM civicrm_contribution ORDER BY receive_date;
SELECT id, contact_id, receive_date FROM civicrm_contribution ORDER BY receive_date DESC;


Check the bottom of both those lists for odd-looking receive_dates, my guess is you'll find one!