Configuration System failed to initialize while trying to connect to web service

I have a Xamarin Android App, made with Visual Studio 2017, and a ASMX Web Service.

The Web Service is published and running in the web Sever, the App, when in Debug mode, connects and runs fine without errors.

When I do the APK file and install it in other device I received the following error when trying to log in (First time the app calls the Web Service).

Configuration system failed to initialize

System.TypeInitializationException: 
The type initializer for 'System.Uri' threw an exception. ---> 
System.TypeInitializationException: 
The type initializer for 'System.UriParser' threw an exception. ---> 
System.MissingMethodException:
Method not found: bool System.Runtime.Versioning.BinaryCompatibility.get_TargetsAtLeast_Desktop_V4_5()
--- End of inner exception stach trace --- 
 at (wrapper managed-to-native)
System.Object.__icall_wrapper_mono_generic_class_init(intptr)
 at System.Uri..cctor () [0x00000] in <988fa07610c94365ae6d295a6aa379fe>: 0
--- End of inner exception stach trace ---
 at System.Configuration.ConfigurationManager.EnsureConfigurationSystem() [0x00022] in <673a29f4914b4711bafe0a24a4318f71>: 0

I already tried the most common answer for this error without any luck.

<configSections>
    <sectionGroup name="applicationSettings"
                  type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >

      <section name="DCSWhseWS.Properties.Settings"
               type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
               requirePermission="false" />

    </sectionGroup>

This is the Web.config I'm using:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <sectionGroup name="applicationSettings"
                  type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >

      <section name="DCSWhseWS.Properties.Settings"
               type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
               requirePermission="false" />

    </sectionGroup>

  </configSections>
  <system.web>
    <customErrors mode="Off"/>
    <compilation debug="true" targetFramework="4.6.1"/>
    <httpRuntime maxRequestLength="10240" executionTimeout="1200"/>
    <pages controlRenderingCompatibilityVersion="4.0"/>
  </system.web>  
  <connectionStrings>
    <add name="ConnString" connectionString="PBlWIpWVxZphTCce55j8P3gOqn3SkHqBx0Mz+F9VDFNMXc+uQ+Blgvg2/dt5W0KjBJe7iDu7C1BNjSxe/f3Vx7aLVBuqLSo41iEzVhXmmShi8LER83ihpN0hbrd8z/XZzwPS0JRqDERPd07SLgWMNg=="/>
    <add name="ConnStringTest" connectionString="NpoUd7klEHdHbMERo/Qfq6gv2bakghTNJCMPuX4gIeIYco7297Narru6dSwNJy0TNpaQ67nlCAGEcAAPTPB0O+R1qTqBuysnlkzxiDnrP8ulzR7U4JiekjyZln8Lb8VNKJf/UIK+MDBPIus8gbNUpg=="/>
  </connectionStrings>
</configuration>

And this is how I call the Web Service from the Android App:

WhseWS.Whse obj = new WhseWS.Whse();
return JsonConvert.DeserializeObject<clsUser>(obj.Login(UserCode));

Again, this error doesn't happen when I'm debugging the app only when the APK is installed in any device.

Thank you very much for the help!