Currently RORB won’t allow you to input a user defined inflow hydrograph if you are running RORB in ARR 2016 mode. The only way to input a user defined hydrograph is through the storm file in a single run. The error you are getting should be because RORB is looking for the hydrograph in the storm file but can’t find it. The format of the storm file to input hydrographs are detailed in the RORB manual, Table 5.2, Item number 9. There are some example storm files in the manual as well as the SampleData folder that comes with RORB.