problems with levelplot and contourplot

Hello,


Using the following code i want to make a level or contourplot of some  
data that I produced

library(grid);library(lattice);

mydata <- read.table("avgee.dat");
mymat <- as.matrix(mydata);
mymat <-t(mymat)
vals<-as.vector(mymat);
conc<-c(0.0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5);
a<- c(0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5,5.0,  
7.5,10, 25, 50, 75, 100);
grid<-expand.grid(x=conc, y=a);
levelplot(vals ~ conc * a, grid, region=TRUE, cuts=20);

When I do this get a blank output window and the following warnings

Warning messages:
1: longer object length
	is not a multiple of shorter object length in: is.na(x) | is.na(y)
2: longer object length
	is not a multiple of shorter object length in: id.na | is.na(var)
3: longer object length
	is not a multiple of shorter object length in: id & if  
(is.shingle(var)) ((var >= levels(var)[[cond.current.level[i]]][1]) &

 >

I've examined this mailinglist and the web and tried the examples other  
people suggested.  They seem to work.
Yet, my code seems the same as

a <-1:10
  b <-11:20
  j <- rnorm(100)
  grid<-expand.grid(a = a, b = b)
  levelplot(j~a*b, grid)

(from a previous mail)


and it does not work.

Can anybody tell me what I'm doing wrong?  Furthermore as you ight  
notice the data in a is in log-scale so I want the y-axis of the plot  
in logscale.