Solvederror 28-2

i got this error in gm games using backdoor hack why?

i dont know maybe its a new error cause i cant seem to find it http://www.mpgh.net/forum/243-crossf...formation.html

ur playing ZM with OHK Knife..Well man, as first dont always play with knife..Kill 6/7 mutants and play with gun for a bit, than with knife for a bit and than again with gun..thats the only soluton for now :S