R help - Jan 2008 - rpart Error in yval[, 1] : incorrect number of dimensions

I am trying to make a decision tree using rpart. The function runs very
quickly considering the size of the data (1742, 163). When I call the
summary command I get this:
> summary(bookings.cart)
Call:
rpart(formula = totalRev ~ ., data = bookings, method = "class")
  n=1741 (1 observation deleted due to missingness)

  CP nsplit rel error
1  0      0         1
Error in yval[, 1] : incorrect number of dimensions


note:
> dim(bookings)
[1] 1742  163


I have run rpart on past projects without any problems. I have used a
catagorical version of the variable totalRev that was partitioned into four
levels (and coded as a factor).

Does anyone have any ideas that might help?

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