Error list for
Peter Webb, Stratifications and Mackey functors I: functors for a single group,
Proc. London Math. Soc. (3) 82 (2001), 299-336.
Page 307 line 9 (third sentence of the proof of 2.5): It should read:
Assuming that $M_{i-1}\subseteq {\rm Im} f$,
In other words, the containment is the wrong way round.
Page 323 line -10: The argument that Coker \alpha_1 lies in D is wrong.
The correct argument is that
Coker \alpha = Coker \alpha_1 \oplus Ker (\gamma\beta)^n.
Since Coker \alpha lies in D, so does Coker \alpha_1, because it is a summand.
Page 324 line -4 (statement of Theorem 9.1): It should read
$Hom(\Theta(\lambda),\Theta(\rho))=0$ unless $\lambda\ge\rho$.
(Clearly the strict inequality > makes no sense here.)