Posts Tagged .Net

Visual Studio: Downloaded Assembly Gives "ValidateXaml" task failed unexpectedly Error or FileLoadException

This is a How To Fix when you have downloaded a foreign (to your computer) assembly which can occur when dealing with Silverlight assemblies but it applies to all assemblies downloaded. Here is more of the errors:

error MSB4018: The "ValidateXaml" task failed unexpectedly.

error MSB4018: System.IO.FileLoadException: Could not load file or assembly ‘… \ImageSequence.dll’ or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)

System.NotSupportedException: An attempt was made to load an assembly from a network location which would have caused the assembly to be sandboxed in previous versions of the .NET Framework. This release of the .NET Framework does not enable CAS policy by default, so this load may be dangerous. If this load is not intended to sandbox the assembly, please enable the loadFromRemoteSources switch. See for more information.

The situation is that the OS has identified that the assembly was not made on the computer and has been blocked. This is usually the case with downloaded assemblies and is a security feature.

Steps To Resolve

  1. In Visual Studio in the Solution Explorer Window right click on the project which contains the dll and select Open Folder in Windows Explorer.
  2. In Windows Explorer find the dll in question and right click and select Properties.
  3. Select Unblock and select OK. (As shown below)


  4. Rebuild.

Once you see the properties and this text its more self explanatory than the Visual Studio error.

This file came from another computer and might be blocked to help protect this computer.


Remember that .Net is an Xcopy install. Meaning that any .Net application can be installed by simply copying over the assemblies. The OS recognizes the assemblies and categorizes them for running. When one copies code over and tries to manipulate it in Visual Studio the OS blocks for safety reasons and it subsequently fails during a Visual Studio build.


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C# WinForms: Monitor Threads, Handles and Bytes on the Status Strip

This article demonstrates how to monitor performance of an application to report items as handles, memory or threads. It demonstrates how to create a status bar with the display of those performance items in real time using C# in .Net 2/3. One can see if the application is leaking any resources in those areas.

Why not have your application provide information to its running state such as handles, threads and the bytes being used. This article will show you how to create a Winform Application with a status bar where each label reports handles, threads and the bytes used.


  1. Create a winform application.
  2. Add the Timer component to the form and set these properties:
    1. Timer: Change the Interval from 100 to 1000 so it ticks off every second.
    2. Timer: Set Enabled to True
    3. Create a event for the Tick event.
  3. Add three PerfomanceCounter Components to the form and name them pcPrivateBytes, pcHandles and pcThreadsBuild the application and run it. Then set the properties below:
    1. All: CategoryName = Process
    2. All: InstanceLifetime = Global
    3. All: MachineName = . (Yes a period)
    4. All: InstanceName = (Find the running application name in the drop down list, hence why we are running it.)
    5. pcHandles: CounterName = Handle Count
    6. pcThreads: CounterName = Thread Count
    7. pcPrivateBytes: CounterName = Private Bytes (Private bytes is only the bytes that the application allocates and not any extraneous bytes allocated by the system)
  4. Close the running application.
  5. Add a Status Strip to the application and create three status label areas named tsslHandles and tsslThreads, tsslPrivateBytes. Note the Private bytes is pretty dynamic, so placing it at the end is a good idea.
  6. In the timer tick event add this code which will get the current values of the performance moniter:
    tsslThread.Text  = string.Format("Threads: {0}", pcThreads.NextValue().ToString());
    tsslHandles.Text = string.Format("Handles: {0}", pcHandles.NextValue().ToString()); 
    // Divide the return of Private Bytes to something we will recognize.
    tsslPrivateBytes.Text = string.Format("Private Bytes: {0}", (pcPrivateBytes.NextValue() / 1000).ToString());
  7. Run the application and you should see this which gives you a running total of what your application is doing.



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Reflect Interface from Unknown Assembly in C#

I had a need to scan a directory for assemblies and load (instantiate) a specific interface from the foreign assembly. The idea was that the application would work with a plugin architecture which would allow for an outside foreign assembly to be dropped in. Upon startup, the application would look into the directory and instantiate the plugin via its interface. (Note this is .Net 2 code and .Net 3.5 has a plugin architecture but the concepts of reflection are what are important in this article).

The following code will accept a filename of the assembly and attempt to load the interface in question. If it succeeds it returns the interface:

private IPlugin LoadPlugin( string AssemblyFileName )
 IPlugin PluginFound = null;
 Type iPluginType = typeof(IPlugin);

 Assembly _Assembly = Assembly.LoadFrom(AssemblyFileName);

 if (_Assembly != null)
   Type[] types = _Assembly.GetExportedTypes();

   foreach (Type t in types)
    if (iPluginType.IsAssignableFrom(t))
     IPlugin operation = Activator.CreateInstance(t) as IPlugin;

     if (operation != null) // Found!
       PluginFound = operation;

   return PluginFound;

Here is what is going on:

  • Line 1 : The fully qualified filename is passed into the method.
  • Line 3 : The instantiated object if found, to be returned in this reference.
  • Line 4 : The actual type we are interested in.
  • Line 10 : Reflect the types found in the foreign assembly.
  • Line 13 : Is the current type the same as what we are looking for?
  • Line 15 : Try creating an instance.
  • Line 17 : Test the cast from line 15. If it is not null. We have a valid instance.

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