The error you're encountering typically arises when the MCS is set too high. Try reducing the MCS to lower values to avoid this issue. Additionally, ensure that the packet size in the Application Traffic Generator is set to a nominal value and not too large. Given that this example uses a 20MHz bandwidth, the allocation of Resource Units (RUs) to downlink stations is fixed based on the number of users, as shown in the table provided in the "Further Exploration" section of the example.
In a 20MHz OFDMA transmission, a maximum of 9 users can be supported with 26-tone RUs. Therefore, if you try to add more than 9 client nodes, there will be no resource units available for additional transmissions.
Hope it helps!
