Due to the trouble with the small blocks and recent stress testing, the owners of MasterXchange find it too difficult to continue. So, these stress tests have resulted in more than one person throwing in the towel. Too bad. Better go withdraw any residual funds you have there.
They seem nice and honest people, they adress their customers beforehand with this message:
Please check your account balances and withdraw your coins before November 15th 2015
I wish MtGox did the same. I wish all exchanges be like this:
We stored millions worth of your mastercoin and maidsafe and were never hacked.
That's a shame it didn't work out for them.