You can’t schedule or start a Skype for Business meeting after the May 2017 CU is installed

Consider the following scenario:

• The May 2017 cumulative update is installed in your Skype for Business Server 2015 front-end server pool.
• Federal Information Protection Standards (FIPS) is turned on in your environment.

In this scenario, users in the updated pool can’t do any of the following:

• Schedule a meeting.
• Start an ad hoc meeting by using Meet Now.
• Start a pre-scheduled meeting.
• Turn a two-party conversation into a meeting by inviting a third user.

The May 2017 cumulative update introduces a meeting functionality dependency on a Cryptographic Protocol implementation. This implementation is in the .NET library of older versions of the .NET Framework and is incompatible with the FIPS guidelines. 

To work around this issue, use one of the following methods.

Method 1

1. Update to the .NET Framework 4.6.2.
   
   Note This is the recommended .NET Framework version for Skype for Business Server 2015.
2. Do a rolling restart of the servers to implement the change.

Method 2

Roll back to a previous cumulative update on the affected pools.