Outlook 2013 client cannot sync Sharepoint 2010 document library

Hi there.

A partner in foreign country is trying to sync a SharePoint 2010 document library with Outlook 2013.

We thought 1stly that the problem is related to Office client, so customer has agreed to upgrade Office 2007 to Office 2013, but we are having the same problem on the latest Outlook client.

Send&Recieve in Outlook client makes an error for SharePoint list with error code: 'SharePoint' reported error (0x80040102) : 'Outlook cannot connect to the SharePoint List (Shared documents). The server may not be reachable from your location. Contact the SharePoint site administrator for more information. HTTP 0.

We have tried thousands of time removing and readding the SharePoint document library to sync to Outlook but it is not working.Thehttps://sharepoint.site.com/ is also added to trusted sites in IE of customer.

any hints how to solve this would be more and then appreticiated.

with best regards,

bostjanc