For this problem there some workarounds but they are only temporary solutions, here you have all that I have tried:
1. Delete the oldest file in the conversation history folder (%userprofile%\AppData\Local\Microsoft\Office\15.0\Lync\sip_EmailAddress\History Spooler) restart outlook and it going to work again.
2. Re-create the skype profile, first sign out and exit from skype and outlook, then go the follow path “%userprofile%\AppData\Local\Microsoft\Office\15.0\Lync\” rename the current sip_EmailAddress (you can add _Old) open skype and outlook and it going to work again.
3. Update the skype for business client.
But the most recent fix is modify the exchange server file web.config. it means open this file from installation directory > Client access > EWS. Edit web.config file and add this line (Preferably type it instead of copy & paste): Restart IIS and it works again.
I hope it helps