Workflow Failed On Start

Recently I tried to create a custom approval workflow using VS2008 with wspbuilder. I successfully deployed the wsp and added the workflow to a custom list, but when I started the workflow I got an error saying: Failed on Start (retrying)

In the SharePoint logfile I found this error:
_{Engine RunWorkflow: System.Workflow.ComponentModel.Compiler.WorkflowValidationFailedException: The
workflow failed validation. at System.Workflow.Runtime.WorkflowDefinitionDispenser.ValidateDefinition(Activity
root, Boolean isNewType, ITypeProvider typeProvider) 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)}

After debugging my workflow I noticed that the error occured in a while loop where I used “Declarative Rule Condition”. The solution for this problem was to edit the Visual Studio project file (using notepad) and add the second line below:

Then I reloaded the project and redeployed the wsp and everything worked :)