When a Lync 2010/2013 desktop client for Windows signs-in, to minimize the bandwidth consumption the Lync client retrieves a lot of information from cache. This cached information is stored in the users SIP Profile in a folder named sip_(SipURI of the user) located on a Windows computer in the following folder:
Lync 2010:Â %UserProfile%\AppData\Local\Microsoft\Communicator\
Lync 2013:Â %UserProfile%\AppData\Local\Microsoft\Office\15.0\Lync
Skype for Business:Â %UserProfile%\AppData\Local\Microsoft\Office\16.0\Lync
If there are any issue with the files in the SIP profile, users might experience issue with Lync client such as:
- Contacts appear to be offline
- Unable to search the Global Address List
- Contacts are missing from the contact list
- Contacts display Presence Unknown
- Presence is not displayed in Outlook or SharePoint
- “User is not SIP enabled” errors
- “Lync Server is Temporarily Unavailable” errors
Additionally, it is a good practice to delete the SIP profile when switching to a new Lync platform as connection information can be cached.
To resolve the issues listed above, use the following guidance to delete the SIP profile for the affected user.  NOTE: Depending on the Windows Explorer settings, the SIP profile folder may be hidden, if you are unable to navigate to the path listed for your version of the Lync client you will need to set Windows Explorer to Show Hidden Files and Directories prior to completing the steps below.
Deleting the SIP Profile
- Close Lync completely by right-clicking the Lync icon in the Windows System Tray and selecting Exit.
- Open Windows Explorer and navigate to the folder that corresponds to the Lync client version that is installed
- Lync 2010:Â %UserProfile%\AppData\Local\Microsoft\Communicator
- Lync 2013:Â %UserProfile%\AppData\Local\Microsoft\Office\15.0\Lync
- Skype for Business:Â %UserProfile%\AppData\Local\Microsoft\Office\16.0\Lync
- Delete the sip_username directory that matches the sip address of the user experiencing the issues.  This directory will be rebuilt when the Lync client is restarted the next time.
- Restart the computer
- Restart the Lync client
The SIP profile folder and cached information will be rebuilt and the issues above should be resolved.