Unfortunately I have to take back my "universal work around". The tested Galaxy S4 can still sends messages and media just fine. I lately tested to send a message from a Galaxy S5 with the same official WhatsApp version... same issues. Also messages from an IPhone 4s with an even older WhatsApp cant be recived. Maybe you have to send a message to every single contact in "symbian-mode", to completely "unencrypt" your chats... Sorry guys