Did I make a mistake?

I recently accepted this internal job for another department. In a
nutshell, it is to setup a small web site. The problem is the work is
not from my department.

I expressed to the IT manager (who is not my direct manager) that I am
interested in doing more work to expand my abilities. My direct report
also knows this. Before accepting this job, I asked for my manager's
permission. He accepted and that is why I'm doing it now.
But now, he is bitching about it (classic 2-faced attitude as
described in previous entries).

I wonder, did I make a mistake accepting this? Is it wrong that I want
to take on more, or better, challenges?

He does bitch a lot.

A couple of months ago, I made another 'mistake'. My manager put me in
charge of an internal move and some thigns didn't go quite as planned.
So I made a complaint about the person in charge of the move, in this
case the office manager, and somehow I decided to include the
Operations manager in the email. I only included the COO because I
feel I know him and we communicate freely in the office. Of course
being COO, he proceeded in investigating the matter which was then
brought back to my manager. The office manager got a formal letter in
her record because of this and I did apologise to her. Certainly not
my intension and it was a mistake. I just wanted for the move to be
done correctly as my manager put me in charge and their satisfaction
is my satisfaction. There is another story to this - my manager
doesn't like the office manager either. In fact, I was closer to the
office manager than my manager ever was and he calls her names and
makes fun of her behind her back. After this incident, he spoke with
the COO and the office manager and made me into the bad guy. He now
pretends to be best friends with her.

Going back to the current situation. If my manager didn't really want
to approve my work with this other department, then why approve it?
I've asked him. I said ..."as my manager, it is up to you whether you
approve it or not" I may want to do it but it is not up to me to
decide.

It is situations like this that makes it difficult to ignore...