To dream of mud means that you are involved in a complex and compromising situation. It is probable that you are in need of some clarity of mind.
To dream that you are walking in mud denotes that you are weighed down and frustrated by certain problems in your waking life.
To dream that your clothes have been smeared by mud signifies that your credibility is being questioned. Consider the term 'mud-slinging' to refer to some political antics.