[jQuery] cyclic __proto__ value error, what is it?

[Giovanni Battista Lenoci]

Hi, I'm  heavily using jquery in a page that loads a lot of things,
and sometimes (apparentily without a sense) firebug shows this error:

cyclic __proto__ value
[Break on this error] eval(function(p,a,c,k,e,r){e=function(c)
{return(c<a?'':e(parseInt(c/a)))+((c=c%a...

On this project I'm using jquery 1.3.

Can anyone help me to discover the cause of this error?

Thank you