There seems to be a discrepancy between the spells Winds of Mundane Silence (ars 5 p 161) and the Perdo Vim guideline it seems to be using (ars 5 p 160):
From Winds of Mundane Silence:
"You can cancel the effects of any spell if, with this spell, you can double the level of the spell on a stress die + the level of your spell."
From Perdo Vim guidelines:
"Dispel any magical effect with a casting total less than [or equal to] half the (level + 4 magnitudes of the Vim spell + stress die (no botch)" (errata text added)
The WoMS refers to the "level of the spell" while PeVi refers to "casting total". Yet it seems that WoMS is based on that PeVi guideline.
Maga Exemplia casts Aura of Rightful Authority, a level 20 spell, with a casting total of 25. Magus Krystos casts WoMS at level 40, succeeds, and on his dispelling roll gets a 2, for a total of 42. Under the WoMS text he dispels the Aura, under the PeVi text he does not.
Maga Exemplia casts Aura of Rightful Authority, a level 20 spell, with a casting total of 15 (she takes 1 fatigue). Magus Krystos casts WoMS at level 30, succeeds, and on his dispelling roll gets a 2, for a total of 32. Under the WoMS text he fails to dispel the Aura, under the PeVi text he succeeds.
There is also a discrepancy in that WoMS lets you botch the dispelling roll while PeVi says you can't.
It doesn't really matter to me which of these is right, but I'd rather there was one standard rather than two.