Switch down to .NET 4.0 since it supports Windows XP still.

ssh-handler/app.config

@@ -0,0 +1,3 @@
+<?xml version="1.0"?>
+<configuration>
+<startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client"/></startup></configuration>

ssh-handler/ssh-handler.csproj

@@ -9,7 +9,7 @@
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>ssh_handler</RootNamespace>
     <AssemblyName>ssh-handler</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <PublishUrl>publish\</PublishUrl>
     <Install>true</Install>
@@ -26,6 +26,7 @@
     <IsWebBootstrapper>false</IsWebBootstrapper>
     <UseApplicationTrust>false</UseApplicationTrust>
     <BootstrapperEnabled>true</BootstrapperEnabled>
+    <TargetFrameworkProfile>Client</TargetFrameworkProfile>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <PlatformTarget>AnyCPU</PlatformTarget>
@@ -81,6 +82,9 @@
       <Install>false</Install>
     </BootstrapperPackage>
   </ItemGroup>
+  <ItemGroup>
+    <None Include="app.config" />
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.