Error message when dissolving polygons

Hi,

I?m trying to dissolve a polygon with 345 municipalities in 56 metropolitan areas. I?m following a tutorial found in the web, now I?m stuck in a step, I got an error message:

input = readShapePoly("zm.shp", proj4string=CRS("+proj=lcc +ellps=GRS80 +datum=WGS84"))
projectedpolygons = spTransform(input, CRS("+proj=lcc +ellps=GRS80 +datum=WGS84"))
zmprojPS = SpatialPolygons2PolySet(projectedpolygons)
plotPolys(zmprojPS, proj=TRUE, col="wheat1", xlab="longitude", ylab="latitude")
print("Calculating polygon areas...")

[1] "Calculating polygon areas..."

attr(zmprojPS, "projection")

[1] "1"

attr(zmprojPS, "projection") <- "LL"
zmPolyAreas = calcArea(zmprojPS, rollup=1)

Error in calcArea(zmprojPS, rollup = 1) : 
  To calculate the areas of polygons defined by longitude-latitude
coordinates, this routine first projects them in UTM.

Attempted to automatically calculate the missing 'zone' attribute, but
that failed because the mean longitude falls outside the range
-180 < x <= 180.

How I can solve this issue?

Thanks in advance,

Rolando Valdez