Note: I have gone with the "two Roberts theory" put forth by Chris Phillips below, this being the elder Robert.
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Curt Hofemann, curt_hofemann@@yahoo.com, in a post-em, states:
Paget's Baronage makes Robert (d. by c.1249) the son and heir of Richard, 3rd son of Manasser, 2nd son of Manasser (living 1156). (I suspected that there might be two Roberts in succession instead.) [Ref: Chris Phillips, message to soc.genealogy.medieval, 19 Jun 2002]
Paget says that the younger Robert's father was a second cousin of the elder Robert, but perhaps this is slightly wrongÖ The common ancestor is said to be Manasser Aguillon, living 1156, who had a son and heir WilliamÖ William had a grandson William (Ö I didn't note the intervening generation), who died shortly before 3 Oct 1244, when his son Robert did homage and had livery [citing Rot. Fin. 28 Henry III, m.2]. This Robert was the younger of the RobertsÖ says Paget.
Going back to Manasser, Paget says he had a second son Manasser, living 1172, and that the younger Manasser had a third son Richard, who married Ela de Frivill or Freville, by whom he had a son Robert. Richard and Robert appear as witnesses in 1201 [citing Cal. Docs. France i no 1403]. Paget says that this son Robert was the elder oneÖ
Paget gives further details of the "elder" Robert's career, from 1203 to 1227, and says he married Agatha, dau and coheir of Fulk Beaufoy [citing Blomefield's History of Norfolk], and says he had 4 daughters by her (repeating some of the errors about the daughtersÖ). He adds that Robert married secondly Alice, widow of John de Wahull (d.1217) [citing Bracton's Notebook, no 1182] and daughter of William de Munchensi, and that Robert was still living 1232.
Having said that, we know that the mother of the "elder" Robert's 4 daughters was not in fact Agatha de Beaufo, but Margery, daughter of William de Fresney. Also that at least two of these daughters gave birth to their heirs around 1240. And that C.J. Phillips in his History of the Sackville Family makes Agatha de Beaufo the mother of Robert, not his wife.
So could it be that there are two Roberts here - the first who was active by 1203 and married Agatha de Beaufo, and the second who married Margery de Fresney and died around 1249 leaving 4 daughters and a widow Alice "de Merley/Marley"? Perhaps this Alice is the same one mentioned above, in any case. [Ref: Chris Phillips, message to soc.genealogy.medieval, 24 Sep 2001]