Jude 9<BR>9 But even the archangel Michael, when he was disputing with the devil about the body of Moses, did not dare to bring a slanderous accusation against him, but said, "The Lord rebuke you!"
(from New International Version)

Matt 18:18-20

18 "I tell you the truth, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.

19 "Again, I tell you that if two of you on earth agree about anything you ask for, it will be done for you by my Father in heaven. 20 For where two or three come together in my name, there am I with them." 
(from New International Version)

One of commontaries that I read puts it this way: 

Jesus' promises in verses 18 and 19 have suffered serious misinterpretation throughout the history of the church, the most extreme being the Roman Catholic doctrine that the church has the divine authority to forgive sin. Many charismatics use these promises--along with others, such as those of Matt 7:7 and 21:22--to claim from God every imaginable blessing and privilege just for the asking.

But in light of the context of what Jesus had just said, in the light of common rabbinical expressions of that day, and in light of the grammatical construction of the text, it is clear that He was not teaching that God's power can be bent to men's will. He was not saying that men can force heaven to do things. Quite to the contrary, His promise was that when His people bend their wills to His, He will endorse and empower their act of obedience.