Liz wrote:

> >52. "Bîaid dano in tsesêrgid Suidi 19) Chaim .i. isre atas tormus
> >dobêrai 20) scêla derbai in toóchaidhe. Môet[h]aighfid cride 21)
> >dûrai arnaisdeis na ndemno 7 inna n-ifernda 22) re ocht .xx." 23) "Is
> >trôcar", or Bricîn.
> I thought ‘in tsesêrgid’ was possibly the nominative singular
> article plus ‘es(s)éirge’ (“re-arising, resurrection”), 

Although the word is not listed in DIL, I still think that we have an 
agent noun "eisérgid" "resurrector" here.

> The phrase ‘isre atas tormus’ doesn’t look like Irish to me, and it
> doesn’t look like Latin either.  

I can do no better than state that this passage must be corrupt. 
Maybe "isre" is a corruption for "as·ére" "he will arise", the future 
of "as·éirig". For the rest I have no suggestion at the moment.

>     The two ‘o’s in ‘toóchaidhe’ look strange to me, 

They rightly did. The missing "d" was really my mistake.

>    Since it seemed to be followed by two genitive phrases, I
> thought ‘arnaisdeis’ must contain a noun.  

Your line of argumentation is correct, the two follownig genitives 
would demand a noun. But "aisndís" is a bit problematic, since in 
MidIr. this would have been "aisnéis" without a "d" (but maybe I am 
wrong here). I am also playing around with the idea that we have a 
verb here, maybe "ar·naisc", "ar·neat" or so, but then the following 
genitives are difficult.