[R] warning message when try to plot lm object

[jz7 at duke.edu]

Dear all,

Suppose "h1.lm1" is my multiple regression object. When I tried to use
"plot(h1.lm1)", I got the following warning message.
---------------------
plot(hla4.lm1)
Warning messages:
1: NaNs produced in: sqrt(crit * p * (1 - hh)/hh)
2: NaNs produced in: sqrt(crit * p * (1 - hh)/hh)
---------------------
Does anyone know Where the problem might come from?

Thanks so much!