Lockdown in sector 4!

I had been praising GMail and recommended it to my friends before I got a “Lockdown in Sector 4!″ error message from GMail.
But I don't know exactly what I did is wrong.
I intended to make GMail my main account other than ISP's account, but I can't do that if it's possible that GMail account is disabled because of obscure reasons.
I think Google should make it clear in advance.
Anyway please my GMail account come baaack!!