I just refreshed my math studies from college. The number of unique 12 element sequences, without repetition, from a set of 90 elements (1-90) is equal to 90 to the 12th power.

So MS Calc says that for 90^12 you would have in total 282,429,536,481,000,000,000,000 sequences. Generating those on random, while constantly comparing the one generated randomly against all other already generated will take ages to finish, even for a supercomputer.

My suggestion would be to read up on permutations and create an algorithm to generate the sequences in order, rather than endlessly generating random ones.

EDIT: Googling "Visual Basic 6 permutations" I got this: http://www.codeguru.com/vb/gen/vb_mi...mbinations.htm