Hi! I'm a new comer.
I have a IWATSU ECS version 3.01 with IX-12IPKTD-E which is controlled by MBU.
The problem is that they work for a certain period then few of them show "Channel Block" on display.
The other TDM phones fine while problem happened.
System Reset needed to resume.
I tested the phone which having such problem in other ECS system, but seems okay!
I really don't know what should I do to fix this!

It depends on how many IP phones you're trying to support in the system. Sounds like you're over-taxing your MBU. You may have to add more MBU channels.
Call your vendor.

I got 24 MBU channels, but only 5 IP phones.
I guess this is caused by the version (I'm not sure!)
Is there anyone encounter such problem before?

If you're only supporting 5 IP phones, there is a configuration problem somewhere.

Are these phones all on site, or are there remotes phones being used? You may also be having a bandwidth problem.

Get your vendor to check this out for you.

Thank you very much!
I'll contact technician from IWATSU.
Hope this can be solved soon.