"An SSL error has occurred" on SkypeShield App

If when trying to login with the SkypeShield App you get the following error:

This indicates something is wrong with the external certificate. Verify that validity of the certificate using one of the many free-to-use SSL checkers (SSL labs for example) 

and test with the Lyncdiscover URL and the External Skype Pool URL

If you get a low grading (B and less in SSL labs) please fix the certificate.

If you are getting a high grade (A\A++ in SSL labs) and still getting this error please contact support.