> library(DMR)
> library(rpart)
> library(rpart.plot)
> library(lattice)
> dtdat <- expand.grid(a1=seq(1, 10, 3), a2=seq(1, 10, 3))
> dtdat$c <- as.factor(ifelse(dtdat$a1<=7 & dtdat$a2<=1, 1, ifelse(dtdat$a1<=7 & dtdat$a2<=7, 2, ifelse(dtdat$a1<=7, 3, ifelse(dtdat$a2<=4, 4, 5)))))
> prp(rpart(c~., dtdat, minsplit=2, cp=0))
Error: box.col: illegal value

library(dmr.clasval)
 library(dmr.stats)
 library(dmr.util)

Description:    Ubuntu 14.04.4 LTS
ii  r-base-core                         3.0.2-1ubuntu1