[R] mplot :how to deal with missing data

[NATALIA F TCHETCHERINA]

Hello all,
I have  data:

           Genes   time rep vart dye         y trt
130911   sa1-d07 030min   1  col   g  9.636244   o
145771   sa1-d07 030min   1  col   r  8.107577   c
93335    sa1-d07 030min   1  ler   g  7.409566   o
94821    sa1-d07 030min   1  ler   r  5.107160   c
10119101 sa1-d07 030min   2  col   g  8.336862   o
11605101 sa1-d07 030min   2  col   r  7.824530   c
725313   sa1-d07 030min   2  ler   g  8.249347   o
740171   sa1-d07 030min   2  ler   r  7.565084   c
1160522  sa1-d07 030min   3  col   g        NA   c
1011922  sa1-d07 030min   3  col   r        NA   o
562232   sa1-d07 030min   3  ler   g  9.974227   c
547362   sa1-d07 030min   3  ler   r 10.341149   o
..................................................
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I would like to get graphs means for two-way factor combinations
I used Rlab package:
> mplot(data$y[which(data$Genes==sa1-d07)],
data$time[which(data$Genes==sa1-d07)], data$trt[which(data$Genes==sa1-d07)])

However, I have the following error message:

plot window will lay out plots in a 3 by 1 matrix 
Error in plot.window(xlim, ylim, log, asp, ...) : 
        need finite 'ylim' values
In addition: Warning messages:
1: no finite arguments to min; returning Inf 
2: no finite arguments to max; returning -Inf 
> 
I think this is because of some y='NA'.
My question is: how I can deal with this problem?

Sincerely, Natalia.