We recently recieved some ‘new’ LG-Nortel 8540 phones that were running the OCS version of Windows Phone and they would not update to Lync 2010 CU6 Phone Edition.We resolved by unapproving the CU6 device update and going back to a previous version (in our case CU5), the phones all upated without an issue. We were then able to approve CU6 and update the phones to the latest software.The full explaination of this odd behaviour is explained here by Jeff Schertz but the brief version is that Microsoft have changed the Root CA that signs the updates (as of CU6) to one that uses SHA1 instead of the older MD5 which is OK for all Lync versions however OCS versions only support MD5 so hence no update.