I'm having some trouble with trading in TF2.

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I am premium and have been for quite some time. In fact I have traded before. Now, for some unknown reason, I am unable to trade. The error screen says exactly this:
"There was a problem sending your trade request. Trading may be temporaraly unavailable or your account may be unable to send trade requests right now." Originaly I thought nothing of it, and went to trade on a different server. When the problem persisted, I went to find help on Steam's help page, which of course, did not help. I came to realize that maybe it was something I did to my account. I have changed my password and name several times. Could that have affected it? If so, please explain. If not, please give any other reasons that may have caused this. PLEASE HELP! (P.S. Sorry this discussion topic is kind of wordy)