ActiveSync stop working.
When you check by:
https://COMPANYURL/Microsoft-Server-ActiveSync
you receive error and not asking login/password
Usually it is happend after exhange update.
C:\Windows\Microsoft.NET\Framework64\v2.0.50727\CONFIG\enterprisesec.config was corrupt.
Move enterprisesec.config and security.config files away and restart IIS.
Once that was done, EMC. OWA and most other problems went away.