[R-sig-Geo] Proj4 - latitude or longitude exceeded limits

[aurelie.tschopp at vetsuisse.unibe.ch]

Dear all,

I am analysing GPS Data from Chad. I need to first project the latitude and longitudes. I use the package Proj4, the function project for this.  
I have 2 devices and with the data of the 1st device, the projection worked perfectly. But with the data from the other device, I got this error message: "Error in project(loc, "+proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m +no_defs") : latitude or longitude exceeded limits"

I found that Chad was UTM 33P (Wikipedia UTM: https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system ), but some people could use the notification 33N: 33 for the zone and N for the North hemisphere. 

My code is: 
loc <- dat[,c("Longitude","Latitude")
loc_Zone33 <- project(loc, "+proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")

Does anybody know where my problem could be?
Thank you
Aurélie