FYI,

I had the same problem with my Yahoo email. I could receive and compose messages, but it would not let me send messages or replies. I would get a "page cannot be displayed" error message. I opened a hotmail account to see if I could send a message but that wouldn't work either. I could send email from Yahoo with my computer at work though. I thought it was an Internet Explorer problem but it was not.

It turned out to be an adware / spyware program that was on my computer. My firewall/anti-spyware/anti-virus program did not detect it, but Microsoft's free beta version of AntiSpyware detected 3 spyware/adware programs on my PC. The 3 programs were called Marketscore.InternetAccelerator, Coolsavings Coupon Manager, and WhenU.SaveNow. One of them was the culprit because after I removed them, I could send email messages from my Yahoo account.

You can download the free beta version of MS AntiSpyware on Microsoft's website.

I hope this information helps someone out there.