Issues with sound and multiplayer option

I have problem with lack of sounds - I've tried some solutions but there are enough. Also - i am unable to connect to my friend's server. Sometimes it connects, but for most of the time i can't join here. I've read the forum and couldn't find a solution for my problem. Thank you for your reply. 
The other problem that i've seen - when i try to connect to the server with default skin i see information included on screen - that "skin is forbidden in multiplayer version".