TX underflow

I am getting TX underflow when I try to transmit 5 bytes fixed pkt length. I am following the code snipped given in CC2510 datasheet. see attached.

Here's my code -

RFST=0X03; //STX 

while(!RFTXRXIF);  //**wait for clear interrupt or write when the bit is set to avoid tx underflow? 
RFTXRXIF=0; // reset and write receiver address
RFD=0x11; //rx1_addr;
while(!RFTXRXIF); //wait for clear interrupt
RFTXRXIF=0; // reset and write data
RFD=0x01; 
while(!RFTXRXIF); //wait for clear interrupt
RFTXRXIF=0; // reset and write data
RFD=0x02; 
while(!RFTXRXIF); //wait for clear interrupt
RFTXRXIF=0; // reset and write data
RFD=0x03; 
while(!RFTXRXIF); //wait for clear interrupt
RFTXRXIF=0; // reset and write data
RFD=0x04;