I found a similar issue when trying to copy purchased music or TV shows between an iMac and a MacBookPro using an ethernet cable connection for speed and wifi turned off. Kept throwing up an error message. Finally turned wifi back on on both machines and the transfer worked at ethernet speeds. I don't know if this is right but it seemed like the machines had to get authorisation from the Apple Store to work.
Again don't know if this will help you but hoping it does
Are you sure you have Home Sharing turned on? (File > Home Sharing > Turn on Home Sharing) It sounds like you have the regular Sharing turned on which is different from Home Sharing. With the regular Sharing, you can't transfer songs. You can ony listen.
Also, what do you mean by different account? For Home Sharing, you must use the same Apple ID and password to work.