In order to generate results for a given AEP of interest you require runs that have been generated using rainfalls either side of that AEP – therefore, to estimate 1 in 100 floods you need rainfalls rarer than 1 in 100. For this reason RORB will not report Monte Carlo results for the first and last AEPs specified in your IFD input.
When downloading IFDs from the BoM website design rainfalls are split into three different tables – Very Frequent, IFD (up to an AEP of 1 in 100) and Rare (AEP of 1 in 100 to 1 in 2000). You will need to download both the IFD and Rare tables and combine them (either in the RORB interface or Excel) and rerun the model to get results for an AEP of 1 in 100.
I hope this helps!