case XPRG_PARAM_NVMCSR_REG:
                        XPROG_Param_NVMCSRRegAddr = Endpoint_Read_8();
                        break;
+               case XPRG_PARAM_UNKNOWN_1:
+                       /* TODO: Undocumented parameter added in AVRStudio 5.1, purpose unknown. Must ACK and discard or
+                                the communication with AVRStudio 5.1 will fail.
+                       */
+                       Endpoint_Discard_16();
+                       break;
                default:
                        ReturnStatus = XPRG_ERR_FAILED;
                        break;