Workflow paused due to error: Unhandled Exception: System.Reflection.TargetInvocationException

Workflow paused due to error: Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.  at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck)  at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache)  at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache)  at System.Activator.CreateInstance(Type type, Boolean nonPublic)  at System.Workflow.Runtime.Hosting.DefaultWorkflowLoaderService.CreateInstance(Type workflowType)  at System.Workflow.Runtime.WorkflowDefinitionDispenser.LoadRootActivity(Type workflowType, Boolean createDefinition, Boolean initForRuntime)  at System.Workflow.Runtime.WorkflowDefinitionDispenser.GetRootActivity(Type workflowType, Boolean createNew, Boolean initForRuntime)  at System.Workflow.Runtime.WorkflowRuntime.InitializeExecutor(Guid instanceId, CreationContext context, WorkflowExecutor executor, WorkflowInstance workflowInstance)  at System.Workflow.Runtime.WorkflowRuntime.Load(Guid key, CreationContext context, WorkflowInstance workflowInstance)  at System.Workflow.Runtime.WorkflowRuntime.GetWorkflowExecutor(Guid instanceId, CreationContext context)  at System.Workflow.Runtime.WorkflowRuntime.InternalCreateWorkflow(CreationContext context, Guid instanceId)  at System.Workflow.Runtime.WorkflowRuntime.CreateWorkflow(Type workflowType, Dictionary`2 namedArgumentValues, Guid instanceId)  at Microsoft.Crm.Workflow.WorkflowHost.StartWorkflowFromType(Guid instanceId, Type workflowType, WorkflowContext context) Inner Exception: System.IO.FileNotFoundException: Could not load file or assembly 'MCS.CRM.SendSMSVersion20, Version=1.0.0.0, Culture=neutral, PublicKeyToken=12782b4081c82c1c' or one of its dependencies. The system cannot find the file specified.  at Compiled.Workflow002275780b4be111a8a4001ec9f274bf.InitializeComponent()  at Compiled.Workflow002275780b4be111a8a4001ec9f274bf..ctor()

Solution :

http://support.microsoft.com/kb/828991