Hi Jennie,
1, before loading hierarchy with your newly added node you need to load master data first, so that new node will be added to the dimension, once that is done then you load hierarchy to "move" the node into the hierarchy. the error message simply means missing master data in the dimension.
2. During the master data load make sure you select the correct hierarchy and key date (if you use TD hierarchy) if you don't select the hierarchy then all master data in the info object will be loaded into BPC.
Andy