Common Causes of Problems in Internal Communications

According to this site, one of the biggest issues in communications is assuming that if you know something, others must know it too:

Perhaps the most common communications problem is managements' (leaders' and managers') assumption that because they are aware of some piece of information, than everyone else is, too. Usually staff aren't aware unless management makes a deliberate attempt to carefully convey information.

http://managementhelp.org/organizationalcommunications/internal.htm