failed to sync some items outlook 2013 and 2016

Hi
Here are a partial log. Some items can't be synchronized et hang the mailbox of the users with Outlook 2013 and 2016
Can you help me ?

2016-02-18 09:04:51,052 ERROR [ZxMobile] [tid=174462;account=*@*.fr;id=2CB8B5222EB94FDDA005AC50FD7A4C00;model=WindowsOutlook15;proxy=192.168.60.15;oip=192.168.49.17;eas=14.0;rid=54687;] sync - Unable to send item 25655 from folder /Inbox) account *@*.fr: java.lang.RuntimeException: java.nio.charset.IllegalCharsetNameException: charset="utf-8"