I found this problem description it's just my case here..
I could not use the Window Liver Writer to publish my blog sometime after March(probably May) this year.
when i finish editing and click the post putton, it returns me an error
"Error attempting to connect to blog at:
The underlying connection was closed: An unexpected error occurred on a send."
I always used the Writer to create my blog, it had worked well for a long time.
I didn't change any setting on either my blog or the WLWriter.
i sincerely hope someone can help me fix this problem...
Blog url: http://kawayipuffer.wordpress.com/