Cannot put lower arm assembly back on!!!

So my dishwasher (less than 5 years old!) has not been cleaning so I figured out how to take it apart and clean the chopper. This has worked before. However, when I got all the way to the end of putting the thing back together, I have been unable to put the lower arm assembly back on! I read tips online that stated that you needed to tighten it counter-clockwise and tried that (which has worked in the past) but now it won’t go back on. What’s the deal!? Thanks in advance.:mad: