After upgrading a PC to Office 2013 (including Lync 2013), one of our systems wasn’t able to screen share with 2010 users.  The user could share her screen with everyone else, but wasn’t able to view any 2010 screens.  After doing some research, it appears to be caused by two Lync updates, KB2760512 and KB2760556.  [more]Unfortunately, Microsoft hadn’t released a fix for these updates, but we were able to make it work by doing the following steps:

  1. Uninstall the two Lync patches and reboot:
  2. Install the updates individually (Install KB2760512 first and reboot, then install KB2760556 and reboot)

Here is a link to another forum that also discusses the issue: