One third of people registered by ACORN were rejected by election officials?

In an article generally defending ACORN against the recent five films released on biggovernment.com, there was this interesting fact.

Last year, ACORN was forced to acknowledge that election officials rejected 400,000 of the 1.3 million people the group had tried to register. . . .

The article does have some other interesting facts about problems with the ACORN sting.