Email Challenges
http://sudokucup.com/node/3103?mode=multiplayer&resid=67722&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67729&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67736&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67740&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67745&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67504&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67512&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67513&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67515&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67517&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=64741&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67520&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67528&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67530&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67135&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67350&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67354&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67454&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67480&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66940&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67052&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67064&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=51724&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67079&oppid=6768&k...
Medium ones:
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67082&oppid=3&k...
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67084&oppid=3&k...
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67085&oppid=3&k...
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67086&oppid=3&k...
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67087&oppid=3&k...
http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=67088&oppid=3&k...
There are nice and usefull techniques used - UR and BUG for more see:
http://www.sudoku9981.com/sudoku-solving/bivalue-universal-grave.php
http://www.sudokuwiki.org/Unique_Rectangles
Hard puzzles:
http://sudokucup.com/node/3103?mode=multiplayer&resid=66929&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66966&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67047&oppid=3&kor=...
Hard puzzles to practice Unique Rectangles technique:
http://sudokucup.com/node/3103?mode=multiplayer&resid=66964&oppid=3&kor=...
Very Hard puzzles (without guessing):
http://sudokucup.com/node/3103?mode=multiplayer&resid=66932&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66969&oppid=3&kor=...
Very Hard puzzles to practice Unique Rectangles technique:
http://sudokucup.com/node/3103?mode=multiplayer&resid=67047&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67049&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=67051&oppid=3&kor=...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66700&oppid=4323&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66700&oppid=4323&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66704&oppid=4323&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66706&oppid=4323&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66236&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66673&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66678&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66681&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66691&oppid=6768&k...
easy http://sudokucup.com/node/3103?mode=multiplayer&resid=66320&oppid=4323&k...
easy http://sudokucup.com/node/3103?mode=multiplayer&resid=48577&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66325&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66327&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66329&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66330&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66332&oppid=4323&k...
medium http://sudokucup.com/node/3103?mode=multiplayer&resid=66333&oppid=4323&k...
hard puzzles tomorrow, i am wasted
Some more challenges, all Medium
http://sudokucup.com/node/3103?mode=multiplayer&resid=65937&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=65965&oppid=6768&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66181&oppid=5025&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66194&oppid=5025&k...
http://sudokucup.com/node/3103?mode=multiplayer&resid=66132&oppid=6768&k...
Thank you! I've send you each time my solving time via PM because it's not possible to see the result of the challenge right now 
And here are some of mine:
Easy one (without using pencilmarks): http://sudokucup.com/node/3103?mode=multiplayer&resid=65820&oppid=1&kor=...
Very Hard (without guessing): http://sudokucup.com/node/3103?mode=multiplayer&resid=65798&oppid=1&kor=...
Easy one (without using pencilmarks): http://sudokucup.com/node/3103?mode=multiplayer&resid=65787&oppid=1&kor=...
Easy one (without using pencilmarks): http://sudokucup.com/node/3103?mode=multiplayer&resid=65771&oppid=1&kor=...
Medium (with pencilmarks): http://sudokucup.com/node/3103?mode=multiplayer&resid=65723&oppid=3&kor=...
Medium (with pencilmarks): http://sudokucup.com/node/3103?mode=multiplayer&resid=65708&oppid=1&kor=...
Easy one (without using pencilmarks): http://cs.sudokucup.com/node/3103?mode=multiplayer&resid=65697&oppid=1&k...
