it works ok for me, maybe check your security settings for something which may prevent you sending files (could be your virus checker)
once you have chosen the file to send, are you clicking OK (just under your e-mail address on the attach page), it will load the attachment and check it for virus's. then return you to the e-mail page where you can type the message then when ready click on send.
maybe you are choosing the attachment and then clicking back on your browser instead of OK.
it is an easy mistake as the page is set out badly (in my opinion).