Hi everyone,

Can someone explain to me what this error message means? -

() : Downdated VtV is not positive definite

I keep getting it after using this code for my data-

> m1<-glmer(a.martiensseni~distance.tree+herbangular.trans+shrubangular.trans+canopyangular.trans+soilangular.trans+leaflitangular.trans+sandangular.trans+woodangular.trans+waterangular.trans+cobblesangular.trans+rocksangular.trans+archaangular.trans+archbangular.trans+archcangular.trans+archdangular.trans+archeangular.trans+alt+slope+start.time+(1|site)+(1|location),family=binomial)
I get that it is to do with my random effects... but I don't understand why there is a problem. 'Site' is just an area known as A,B,C,D or E and location is the location within the site the frog was found, so either transect 1,2, or 3. I am trying to analyse frog presence or absence data with habitat characteristics... can anyone help????

Thanks Vicky :)

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