tranny grinds when shifting at high rpm

i have a b&M short shifter and everytime i shift and redline 1st to 2nd it grinds in 2nd sometimes i cant even put it in gear… and occionally in 3rd gear… it never used to do that with my stock shifter… does anybody have this problem and fixed it?? i searched and found many similar problems, but did not find any answers… tia