I'm new to CiviCRM, just installed 4.6.5 on my Joomla 3.4.4 testsite. Other software levels:
I tried to import contacts, 980 in total, using a .csv file. There are no duplicates in that file.
At the first try it imported some 250 contacts, then stopped. Second try it imported another 250 contacts, third try another 204 so now I have 704 contacts in my database. Everything that's in that database looks fine.
At the end of each import job it failed with the following message:
/administrator/components/com_civicrm/civicrm/Civi/Core/Transaction/Manager.php on line 107
Somewhere I read I should clear the CiviCRM cache, so I did. I thought maybe a cache problem with approximately 250 contacts. Wrong. Result: now it fails immediately with this message.
My next step will be to upgrade CiviCRM to 4.6.8, but will that help?