Extracting raster values to polygon: error "arguments imply differing number of rows:1549, 0"

Question

I am trying to extract the mean of a raster data to polygons with the following code:

library(rgdal)
library(raster)
library(maptools) 

agri_suitability=raster("suit")
regions <- readShapeSpatial("Regions.shp") #SpatialPolygonsDataFrame

plot(agri_suitability)
plot(regions, add=T)

polygon_agri_suitability=extract(agri_suitability,regions,fun=mean,na.rm=T)
regions@data = data.frame(regions@data, polygon_agri_suitability)

write.csv(regions,"suitability_mean.csv")

After data.frame I get an error:

arguments imply differing number of rows:1549, 0

My "Regions.shp" file in fact includes 1549 rows. But I don't know what this error means and how I can solve it.

Answer 1

_{Thanks to @AndreSilva, I found the problem and the solution.}

The problem was that the polygon and raster layers had different geographic systems. So I used Data Management Project tool of ArcMap to get both layers in WGS 1984. Now, the polygon layer exactly overlaps with the raster map, and the code works correctly.