Why can't I post to my groups from my hotmail account?

I am having problems posting to the yahoo groups that I am a member of from my hotmail email address. I receive mail fine and I can send the word test in the subject line but I can't compose any emails. Also it will allow me to reply to any group members but I can't post. except for one group Urscene-fm@yahoogroups.com.
Why can't I post to my groups from my hotmail account?
maybe it has to do with the groups itself, than the use of hotmail although hotmail seems to often conflict with Yahoo groups. what happens when you try to post? does it come back to your inbox as an error and if so, what does the error state?