NPS MMC Crash after adding new RADIUS client

Hi,

i'm working on a Windows 2008 SP2 version
When i try to add a new RADIUS Client the MMC snap-in stopped working.
i'm also unable to remove old RADIUS clients.

the following error is shown:

Description:

Stopped working

Problem signature:

 

Problem Event Name: CLR20r3
Problem Signature 01: mmc.exe
Problem Signature 02: 6.0.6002.18005
Problem Signature 03: 49e02760
Problem Signature 04: npsui
Problem Signature 05: 6.0.0.0
Problem Signature 06: 4791ade7
Problem Signature 07: 13a
Problem Signature 08: f8
Problem Signature 09: System.UnauthorizedAccess
OS Version: 6.0.6002.2.2.0.274.10
Locale ID: 1043