Why did pope gregory vii and henry vi come into conflict

In the 11th century Pope Gregory VII excommunicated the Holy Roman Emperor, Henry IV. Their disagreement was about who had the right to appoint church officials. When he excommunicated Henry IV, Pope Gregory also told Henry's vassals (noblemen who rented the Emperor's lands) that they did not need to give their support to the Emperor anymore. Once the pope had told them that they did not owe anything to Henry, the German vassals staged a revolution. Henry was forced to give in and he had to go to Pope Gregory to apologise. The pope left Henry standing for three days in the snow before he would see him. When things returned to normal, however, Henry went to Rome and threw the pope out. Gregory was forced into exile, and he died in Salerno in 1085