Sending trade offers

probably

Are you sending them through the client or the site? I used to have this problem when I'm sending offers through client but never when sending through the site.

Yeah, i'm also having a lot of problems with trade offers during this morning...

Like others have said it normally only works properly in your browser, even then it'll send the same trade offer 4 times despite giving you an error, same goes for when you accept them, you'll get an error but it'll still go through.
If for some reason you can't use your browser for trade offers you could delete all (1 or 2) files from you steam folder starting with "ssfn",
this will prompt you to enter your steamguard security code once you open up the steam client again but it WILL NOT lock you out of your ability to trade since the device is still the same, after you enter your code you should be able to send trade offer but only for a short time, probably until the next day or when you reboot your rig again.

Yeah, me too. I'm having problems with trade offers, can't send.
Through steam client or website, not working any of them.

Steam API tango down !