  In the $Activation$ $k$ $Disjoint$ $st$-$Paths$ ($Activation$ $k$-$DP$)
problem we are given a graph $G=(V,E)$ with activation costs
$\{c_{uv}^u,c_{uv}^v\}$ for every edge $uv \in E$, a source-sink pair $s,t \in
V$, and an integer $k$. The goal is to compute an edge set $F \subseteq E$ of
$k$ internally node disjoint $st$-paths of minimum activation cost
$\displaystyle \sum_{v \in V}\max_{uv \in E}c_{uv}^v$. The problem admits an
easy $2$-approximation algorithm. Alqahtani and Erlebach [CIAC, pages 1-12,
2013] claimed that Activation 2-DP admits a $1.5$-approximation algorithm.
Their proof has an error, and we will show that the approximation ratio of
their algorithm is at least $2$. We will then give a different algorithm with
approximation ratio $1.5$.
