I'm finishing the challenge window but right now there is a lot of work on SC9 so here are some challenges just for fun before you'll be able to create your own:
http://sudokucup.com/node/2917/?mode=multiplayer&resid=56212&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=56211&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=56210&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=56209&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=56206&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55637&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55633&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55378&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55376&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55080&oppid=3&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=55066&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=54771&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=54772&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=54245&oppid=1&kor...
http://sudokucup.com/node/2917/?mode=multiplayer&resid=53984&oppid=1&kor...