R Error, very odd....

I'm trying to analyse some excel data in R.  The problem is that when i
input the data with the first column as absolute values, everything works
fine, can analyse as normal.  When I leave the first column unchanged to
import negative numbers as well I get:

Error in storage.mode(y) <- "double" : 
  invalid to change the storage mode of a factor
In addition: Warning message:
In model.response(mf, "numeric") :
  using type="numeric" with a factor response will be ignored