Exception Illegal value in Firebug

Today, I've found exception in m开发者_如何学JAVAy firebug console:

uncaught exception: [Exception... "Illegal value" nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)" location: "JS frame :: http://portal.aolcdn.com/p5/_v39.5/js/main.js :: anonymous :: line 196" data: no]

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This happens for example happen you pass undefined (instead of a string) as an URL to an XmlHttpRequest object. The object detects that this is an invalid value and throws an exception. The exact cause of the problem depends on the code at that position.

Inspect the values of the variables that are used there and see if any of them contain unexpected content.