I have replied to your post earlier in the other thread. Here is the reply again:

Please follow the steps given in the attached file and proceed further. This is a dummy organization. If you wish to create a proper inventory organization then you can follow my Purchasing videos.
If you are able to save the work then I dont see any issues at this point. Simply move forward. Go to Financial Options and see if the inventory organization is appearing in the list of values. If not then we have an issue, otherwise we are good.