A critical buffer overrun occured

When receiving a larger file over zmodem, I get a "A critical buffer overrun occured" after about 222kb of the file is received.   I notice the program gets a bit erratic before the error.

These are the flowcontrol settings I'm using:
    //Setup Hardware flow Control aka fcRtsCts
    vaComm.FlowControl.OutCtsFlow := True;
    vaComm.FlowControl.OutDsrFlow := false;
    vaComm.FlowControl.ControlDtr := dtrDisabled;
    vaComm.FlowControl.ControlRts := rtsHandshake;
    vaComm.FlowControl.XonXoffOut := false;
    vaComm.FlowControl.XonXoffIn := false;
Any help is appreciated.