spsample Error

I'm using spsample() with a second SpatialLinesDataFrame
but now I'm geting an error. This is what I do:

fl2300 <-
readOGR(dsn="/media/Transcend/MONTSENY2008/MONTSENY_UAV2/flMatagalls300",layer="flMatagalls300") 

wpMata300 <- spsample(fl2300[1,],33,offset=0.0,type="regular")

Error in proj4string(x) :
  proj4string only works for class(es extending) Spatial

Nothing looks wrong with fl2300 (at least not different to other SPDFs 
for which
spsample() works fine):

str(fl2)

Formal class 'SpatialLinesDataFrame' [package "sp"] with 4 slots
  ..@ data       :'data.frame':    2 obs. of  2 variables:
  .. ..$ Code   : int [1:2] 1 2
  .. ..$ Comment: Factor w/ 2 levels "CarrElBrull700",..: 2 1
  ..@ lines      :List of 2
  .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
  .. .. .. ..@ Lines:List of 1
  .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slots
  .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 445816 449071 449071 
4628083
4629045 ...
  .. .. .. ..@ ID   : chr "0"
  .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
  .. .. .. ..@ Lines:List of 1
  .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slots
  .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 445983 444326 444326 
4628196
4630060 ...
  .. .. .. ..@ ID   : chr "1"
  ..@ bbox       : num [1:2, 1:2] 444326 4628083 449071 4630060
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "r1" "r2"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
  .. .. ..@ projargs: chr " +proj=utm +zone=31 +ellps=intl +units=m 
+no_defs"

Is this a bug? Do I have anything wrong in this object?
Thanks

Agus