Creating tiff with 1200 dpi

Hi all,

I am trying to create images in R suitable for journal publication. I'd
like to make an image that is 3.6" wide and 5.08" length, and 1200 dpi. 
When I create a tiff file that is 800 dpi and 4x4", it works (although
doesn't look good).
But when I create a tiff that is the size and dpi I want, it doesn't
work. I get the following error:

Error in tiff(filename = "C:\\Documents and
Settings\\sheppardj\\Desktop\\Manuscripts\\Figure 6c.tif",  : 
 unable to start tiff() device

In addition: Warning messages:
1: In tiff(filename = "C:\\Documents and Settings\\sheppardj\\Desktop\\
Figure 6c.tif",  :
 Unable to allocate bitmap
2: In tiff(filename = "C:\\Documents and Settings\\sheppardj\\Desktop\\
Figure 6c.tif",  :
 opening device failed

I've tried the same thing with jpeg, and still get the same error. I've
tried Cario, but I get an error that tiff bitmap is not supported.

Any help would be appreciated. Here is my code. 

#Creating dataframes
new.data2<-expand.grid(FCOND=23.5, FPC1=-0.68, MCOND=22.4, MPC1=-0.82,
RANK=c(6:15))
new.data3<-expand.grid(FOCND=39.1, FPC1=0.46, MCOND=7.4, MPC1=1.3,
RANK=c(4:16))
x2<-data.frame(mod.avg.pred=c(0.28, 0.26, 0.24, 0.23, 0.22, 0.21, 0.20,
0.19, 0.19, 0.18),
uncond.se=c(0.17, 0.15, 0.14, 0.14, 0.15, 0.16, 0.18, 0.19, 0.20, 0.21))
x3<-data.frame(mod.avg.pred=c(0.19, 0.22, 0.26, 0.32, 0.39, 0.47, 0.54,
0.61, 0.66, 0.70, 0.73, 0.75, 0.77),
uncond.se=c(0.18, 0.17, 0.16, 0.14, 0.13, 0.14, 0.18, 0.22, 0.24, 0.26,
0.27, 0.28, 0.28))

#creating a graph that works
## you'll have to direct this file to your own computer

tiff(filename = "C:\\Documents and Settings\\sheppardj\\Desktop\\ Figure
6b.tif",

width=3200, height=3200, units = "px", res = 800)
par(mfrow=c(1,1))
par(mar=c(6,6,2,2))
plot(x2$mod.avg.pred~new.data2$RANK,cex.main=2,main="",
ylab="Brood Survival",type="b",ylim=c(0:1), xlab="Male Plumage Score",
pch=17, cex=1.5,cex.axis=2,cex.lab=2.5)
points(x3$mod.avg.pred ~ new.data3$RANK, pch=19, col="gray45", cex=1.5,
type="b")
lines(new.data2$RANK, x2$mod.avg.pred + x2$uncond.se,lwd=2, lty=2)
lines(new.data2$RANK, x2$mod.avg.pred - x2$uncond.se,lwd=2, lty=2)
lines(new.data3$RANK, x3$mod.avg.pred + x3$uncond.se, lwd=2,lty=2,
col="gray45")
lines(new.data3$RANK, x3$mod.avg.pred - x3$uncond.se,lwd=2,lty=2,
col="gray45")
legend("topleft", c("Large Males", "Small Males"), pch= c(19, 17), col=
c("gray45", "black"), lwd=2, cex=1.5)
dev.off()

#creating a graph that works
## you'll have to direct this file to your own computer

tiff(filename = "C:\\Documents and Settings\\sheppardj\\Desktop \\Figure
6c.tif",
width=4320, height=6096, units = "px", res = 1200)
par(mfrow=c(1,1))
par(mar=c(6,6,2,2))
plot(x2$mod.avg.pred~new.data2$RANK,cex.main=2,main="",
ylab="Brood Survival",type="b",ylim=c(0:1), xlab="Male Plumage Score",
pch=17, cex=1.5,cex.axis=2,cex.lab=2.5)
points(x3$mod.avg.pred ~ new.data3$RANK, pch=19, col="gray45", cex=1.5,
type="b")
lines(new.data2$RANK, x2$mod.avg.pred + x2$uncond.se,lwd=2, lty=2)
lines(new.data2$RANK, x2$mod.avg.pred - x2$uncond.se,lwd=2, lty=2)
lines(new.data3$RANK, x3$mod.avg.pred + x3$uncond.se, lwd=2,lty=2,
col="gray45")
lines(new.data3$RANK, x3$mod.avg.pred - x3$uncond.se,lwd=2,lty=2,
col="gray45")
legend("topleft", c("Large Males", "Small Males"), pch= c(19, 17), col=
c("gray45", "black"), lwd=2, cex=1.5)
dev.off()