Some months ago we discussed how the highly awaited Exchange 2013 Service Pack 1 release was breaking many 3rd party Exchange applications:
Getting 3rd Party Applications to work with Exchange 2013 SP1

Service Pack 1 (aka Cumulative Update 4) is now superseded by the latest Cumulative Update release CU5 which is available for download from:
Cumulative Update 5 for Exchange Server 2013 (KB2936880)

CU5 fixes this problem keeping those critical add-ons running. Being a complete build, CU5 does not require the installation of SP1. Hence if SP1 is not yet installed we can avoid the problem altogether by moving directly to the latest CU.