It is a warning to say that a member has more than 100 children and it is dynamic.
You can ignore it. It is not creating any issues. (It probably was an issue in earlier releases of Essbase where a small RAM was there on the server)
>>Change the child members as "Dynamic Calc" and try to save the outline
^^^Are you sure you want to do this? Is the goal to make the error message (which as has been pointed out ain't much of an error) go away or to store the data points that are needed. I wouldn't change level zero stored members to Dynamic Calc just to make the message stop. I would guess that the members that are under the dynamically calculated parent are there for a reason.
Now if you are saying that maybe it makes sense to introduce hierarchy under that 100+ children parent, then yes, I understand and agree with what you are saying. Why would you have 100+ children under a parent -- that is a lot to navigate.