warning messages by fitting environment vectors in NMDS

Dear list users,

I rund a NMDS ordination analysis with MetaMDS (of vegan)
and afterwards I tried to fit the environmental vectors
onto the ordination.
I run it with envfit function with 1000 permutations.

envfit(nmds1, env, permu = 1000)

I got a message:
"There were 50 or more warnings (use warnings() to see the
first 50)"

and the warnings were mostly:
"In decostand(heads, "norm", 2) : result contains NaN,
perhaps due to impossible mathematical operation"
" In cor(Hperm, take) : the standard deviation is zero"

I got however a list with the Vectors (environmental
variables), r2 and Pr values as well as the factors (in my
case the vegetation plots).

The question is: 
Are the results reliable despite those warnings?
or is the permutation procedure not completed? if not, why?

Thanks in advance!
Cristabel.



Cristabel Dur?n Rangel. PhD Student.
Institute of Silviculture. Faculty of Forest and
Environmental Sciences. University of Freiburg.
Telf: +49 (761) 203 8604 (ofc) 

?Man lernt die Physiognomie einer Landschaft desto besser
kennen, je genauer man die einzelnen Z?ge auffa?t, sie
untereinander vergleicht und so auf dem Wege der Analysis
den Quellen der Gen?sse nachgeht, die uns das gro?e
Naturgem?lde bietet.?
				Alexander von Humboldt, 1799