Please check your database connection. It may be closed.
Sometimes runtimes .NET framework has changed the way that it binds to older mixed-mode assemblies and getting stuck. Use the following attribute in your App.config which is useful if your application uses legacy activation paths.
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>