Error with adehabitatHR and kernelbb

Dear all,

I'm trying to get a Brownian bridge kernel (kernelbb) for each combination of two consecutive animal locations (see commands below) and put them, with a loop, inside a list. It works well at the beginning but after 42 runs, it appears the following warning :

Error in seq.default(yli[1], yli[2], by = diff(xg[1:2])) : 
 invalid (to - from)/by in seq(.)

I looked at the coordinates, at the id, at the time of the run 43 and it's all good...

I looked on the net and it happened to only one person and there was no answer to his post. 

Someone could help me?

## commands

BBtraj <- list()
for (i in 1:(nrow(loc at data)-1)) {
BBtraj[[i]] <- kernelbb(as.ltraj(loc at coords[i:(i+1),], date=loc at data$time[i:(i+1)], id = as.character(loc at data$id[i:(i+1)]),
typeII = TRUE), sig1=as.numeric(as.character(loc at data$sig1[i])), sig2= 5, grid = 1000)
}