I thought I'd solved the matter by starting a new character, I had 13 hours gameplay with a single CTD & a few 'textures not loading' issues.
Then I hit this gamebreaker:-
On the early main quest "Dragon Rising" (MQ104), as soon as I investigate the corpse of Mirmulnir, the following occour ...
1) There are TWO instances of "Fus" in my shout-list, both activated, but one will not complete the 'use your shout' optional sub-quest.
2) The map-marker for Dragonsreach dissapears
3) every time I try to enter Dragonsreach main door, instant CTD.
If I do not investigate the corpse, I can enter Dragonsreach with no problem - but I can't complete the quest. If I console "setstage MQ104 160" the quest does complete, I get the axe of Whiterun etc but when I go to Dragonsreach the Jarl won't give me the next quest, he just asks for proof the dragon was killed. Waiting in a safe-house for 10 days makes no difference btw. (My re-spawn times are reduced by PISE)
I've made at least 3 attempts, from earlier saves, to try for a different outcome but no joy. I've FAR too many manually-installed modz to even think about attempting a one-by-one strategy but I've not added anything significant since 1.4.27 & had no problems with anything back then.
If anyone has any insights ffom similar experiences of their own, or even have a console command for removing shouts ( I checked the wiki, I can't find one) I'd be most grateful.

