String Trimmers

I have a recently purchased PP125, I have used it twice. I detached the edger to attach the trimmer, and I cannot get it to reattach properly. I cannot get the small steel ball on the end of the attachment to get into the whole. It gets within about .5" vertically, but it will not go any further. This unit was running great until I tried to change the attachment. Any ideas would be greatly appreciated...