I can't send or forward email?

I can open my email, through yahoo, and read my mail and move it to different folders. When I try to compose a new email or forward an email, nothing happens. As soon as the new compose page opens or the forward page opens, a small yellow triangle appears in the bottom right corner of my screen and it says, "Error on Page" next to it. I can type my message and add address's from my address book, but when I hit send, nothing happens. I can log onto my email from my work computer and send, compose, and forward all my emails from the same account, but not from my home computer.