Members like you are slowing killing me, i'm not even joking. I answered your question after resizing the enormous pic you embedded, i mean who asks a question and then doesn't check to see if it was answered, and then goes to ask it again in the same forum. Also this exact same question has been answered in a variety of different ways depending on how the member had failed to follow the directions all of these have your question and at least one of them have the answer you need, if you were wondering what type of sorcery i used to find all of this: i clicked search and typed could not find main class...... >.>

you asked here on the last page, where i gave you two possible solutions http://www.worldofminecraft.com/Minecraft_Custom_Client_Wrapper_Download
you could have bumped this http://www.worldofminecraft.com/node/7050
and here although this was technically a different question yours was answered in the first comment ->
http://www.worldofminecraft.com/node/6661
a solution was given here with another possible cause
http://www.worldofminecraft.com/node/4784
a solution to yet another possible cause
http://www.worldofminecraft.com/node/2590

I apologize for sounding so rude, i didn't realize you responded to my answer :(
Try watching this video and following all the steps as closely as possible
http://www.worldofminecraft.com/node/548