Can you try this simple script please?
For me it gives this error:

#!/bin/bash
[ "$PLAYONLINUX" = "" ] && exit 0
source "$PLAYONLINUX/lib/sources"
PREFIX="DotNet35Test"
POL_SetupWindow_Init
POL_Wine_SelectPrefix "$PREFIX"
POL_System_SetArch "x86"
POL_Wine_PrefixCreate "1.5.18"
POL_Call POL_Install_dotnet35
POL_SetupWindow_Close
exit