Spark to MSN Error? thanks

Hi,every one:

when I use IMGate 1.2.4d plugins, and enable an AD group named KF_MSN to use Spark connect to MSN. I have some problems:

At first ,it works well.

After the users in KF_MSN is over 600, login Spark,I can not see the button of MSN. (I am in group KF_MSN )

can you tell me why ,thanks.