Lync/Skype: “Cant sign in to Lync/Skype – There was a problem acquiring a personal certificate required to sign in”

The Problem

Lync/Skype Error message when signing in:

“Cant sign in to Lync – There was a problem acquiring a personal certificate required to sign in. If the problem continues, please contact your support team”.

The Solution

Uninstalling and reinstalling Office 365 software is not going to help you.

There are a couple of solutions here. If one doesn’t work for you – keep going and try the next one. 

Solution 1

Open Lync/Skype login window, and click on “delete my sign-in info”. Then – type in the login details and password again and try to log in.

Lync/Skype delete my sign-in info

Solution 2

Clear Lync’s cache:

1. Go to “C:\Users\Username\Appdata\Local\Microsoft\Office\15.0\Lync (or Skype)\” and delete the specific user’s sip (Session Initiation Protocol) folder.
2. Go to “C:\Users\Username\Appdata\Local\Microsoft\Office\15.0\Lync (or Skype)\ Tracing\” and Delete All files. DO NOT DELETE ANY FOLDER.
3. Open the registry editor (Start + R -> type regedit -> Enter), go to “HKEY_CURRENT_USER\Software\Microsoft\office\15.0\Lync (or Skype)” and delete the specific user’s expandable sip profile folder (the one that contains the user’s email address to sign in to Lync (or Skype)):

Clear Lync’s cache

Solution 3

I actually just did all 3 steps at once versus doing each one at a time and it worked great for me.

As part of clearing Lync’s (or Skype’s) cache, we also need to delete the RSA (encryption key). In order to do that:

1. Exit Lync/Skype.
2. Go to “C:\Users\user\AppData\Roaming\Microsoft\Crypto\RSA.
3. You’ll see one or many folders (defends on how many users logged in to their account on the computer). Delete all the folders.

4. Try to log in.

Don’t forget that if you delete all the folders, each and every user will have to sign in again.