I think it is possible he is the son of Roger->who was the son of Robert
The Peerage_______________
http://thepeerage.com/p46695.htm#i466946
Roger le Bigod died in 1071.1
Child of Roger le Bigod
Roger le Bigod+1 b. b 1071, d. 8 Sep 1107
I've seen that sometimes Robert "the Chamberlain" Bigod is listed as Roger Robert Bigod. I wonder if that is what the confusion is. Not so say it's correct, but most sites list Robert. The dates appear to be the same whichever name is used. If we have some additional information on this, I'd be happy to change it, but I think we'll need a more authoritative source to clarify the ancestry. He's my 22nd GGF. :)