Middle button disabled within ICEM

Rikio

To colleagues with same experience: When i did mesh within ICEM 10.0 a few months ago, the middle button disabled sometimes, i.e. can not be usd to apply operation such as delete after selection. It is so labor consuming that i had to click on the APPLY button to apply. One day, i found the middle button enabled. It is more easy to mesh models. But now, it disabled again. I did not set anything, and just exited and openned the program. Anyone have the same experience? And any solution to enable the middle button?

Thanks

Rikio