What is the one problem for the male and female reproductive system?
I am not sure what you are asking here or if you are talking about plant or animals.
For plants if there are both male and female plants and they are on separate plants the problem that might occur is how the gametes can get together - in other words how will pollination occur. The plant world has solved this in many ways such as air pollination, insect pollination etc.
For some animals such as those that are not very mobile this problem is similar. For most animals the issue is not finding each other but the timing and making sure that they are breeding with the correct species. Animals have worked this out through things such as mating displays, pheremones, and timing the reproductive cycles.
AS #sansatschool says..you need to state which type as in humans or plants. producing asexually or sexually