Adding text in the panels for Trellis plot ...

i was trying to do a for loop for plotting the histograms , but it doesnt
work properly

library(lattice)
columns <- 8:153
plots <- vector("list", length(columns))
j <- 0
for (i in columns)

+ {
+ ? plots[[ j <- j+1 ]] <- histogram( ~ data[,i] | data[,2],ylab =
"Frequency",
+ ? xlab = "Score", xlim = c(1,5), ylim = c(0,100),layout=c(3,1),
+ ? main = c(colnames(data)[i],"index",j+1),mycolors =
colors()[c(536,552,652,254,26)],
+ ? panel = function(..., col, mycolors) {
+ ? panel.histogram(..., col = mycolors[panel.number()])})
+ trellis.focus('strip', 1, 1, highlight=FALSE)
+ ltext(0.60, -0.25, 'PPM', col='blue', pos=3)
+ trellis.unfocus()
+ }
Error in grid.Call.graphics("L_downviewport", name$name, strict) :
?Viewport 'plot1.strip.1.1.vp' was not found

print(plots[[1]])

I am not sure what was happeneing. . . can anyone help me ?