[amibroker] plot text strange behaviour

[murthysuresh]

Hello
when i use this code to do the plot text, it appears for a sec on 
loading and disappears. not sure how to troubleshoot this one.

index =LastValue( ValueWhen(DateNum()==1070829 AND TimeNum()>=100900 
AND Ref(TimeNum(),-1)<100900, BarIndex()));
PlotText("buy",index,10.60,colorGreen);