a) Some frequent "communication freezers" at workplace are: information overload, emotional disconnects and not listening properly. These are typical mistakes in the communication of managers or leaders. When these things happen, employees may not know how to react, they could interpret instructions mistakenly or they could simply limit their potentials because of the lack of rapport. In other words, communication errors in leaders have a high cost in workplace, indeed.
b) Lack of straightforwardness and active listening: What some people take for rudeness is really directness and it is certainly a strength in communication. I tend to use so many roundabouts. In other words, I "beat around the bushes". On the other hand, the lack of active listening skills, that is fully concentrating on what is being said is also a personal barrier in effective communication. Both aspects are weaknesses which in the past affected negatively my performance in groups of study or work in which I had to make my point or justify an idea based on others' opinions. In these situations, all my "communication freezers" were quite evident.
I believe these and other communication skills can be improved through self-awareness and emotional intelligence.