Found this thread and I looks like my problem is of this kind:
http://www.alteraforum.com/forum/showthread.php?p=8500 Well, this article is above my knowledge.
Followed Guideline#4 and got less warnings, but I still have got these:
Info: Minimum slack time is -8.105 ns for clock "CLOCK_24" between source register "SCN" and destination register "Scan:Scanner|LastBrickTemp[2]"
Info: Minimum slack time is -7.876 ns for clock "CLOCK_24" between source register "SCN" and destination register "Scan:Scanner|LastBrickTemp[3]"
Info: Minimum slack time is -7.681 ns for clock "CLOCK_24" between source register "SCN" and destination register "Scan:Scanner|LastBrickTemp[1]"
Info: Minimum slack time is -6.995 ns for clock "CLOCK_24" between source register "Scan:Scanner|BIT0" and destination register "Scan:Scanner|LastBrickTemp[0]"
Info: Minimum slack time is -4.697 ns for clock "CLOCK_24" between source register "Scan:Scanner|INIT" and destination register "Scan:Scanner|LastBrickTemp[0]"
Happy for any kind of answer.
Cheers