"Error in theta.ml: ..." ? ? ?

[<msc0235@geo.ed.ac.uk>]

Dear all,

does any one know what the error message below means  - and how I could fix
that ?
 the data is a bit sparse, but I thought the glm.nb should take care of
that. The model I was trying is:
adults <- glm.nb(adults ~ x.coord + sheep + grouse, data = LS, trace = F,
maxit = 50)

Error in theta.ml: Missing value where logical needed: while((it <- it + 1)
< limit && abs(del) > eps) {
 t0 <- abs(t0)
 del <- score(n, t0, mu, y)/(i <- info(n, t0, mu, y))
 t0 <- t0 + del
 . . .


thanks a lot!


Helene