Ah, great info. It should normally take a second or two. Could you try logging out and in again at Project-GC?
The code has been rewritten just a few weeks ago, so there might very well be an unknown issue. If so, we will have to dig into that.
By glancing at the code there seems to be 3 major reasons to return an error.
1) Not logged in, which a logout/login will fix. The site might partially think that you are logged in.
2) The button has been used the last 7 days before. It should then be disabled (light blue) already, and not clickable. In my test case I did now, that seems to work properly.
3) Captcha error. In this case the button should reset back to the original text and the captcha input field border shall turn red.
The first two errors aren't handled very well and the effect you are seeing will happen. The button will be stuck at "sending".