In december 2008 I had the same experience. Flying on CO from IAH toIAMS.
Firstly I was allowed to enter. After 30 minutes they told me they closed for cleaning.
When I came back in one hour, access was not granted anymore.
Because I was not on the afternoon business-flight only.

I asked FB in Amsterdam about their opinion. They told me I had official access.
They told also my complaint was sent to Houston and FB would keep me updated.
Which (ofcourse?) never happened.