In my test evironment, just like that, the workflows on a document library sotp working. Normally it starts on creation of a new document and the other can only be started manually. None of them worked anymore.
So what I did to resolve the problem was to remove the workflow from the library together with the complete history of the workflow. Then I opened the SharePoint designer and associated the workflows again with the list. Problem solved. I don't know why it happened, but for all I can google its a bug in SharePoint.
Workflow possibilities with Microsoft
Microsoft offers default 3 possibilities:
VS 2005, Sharepoint designer and out of the box solutions.
v Out of the box solutions: By default there are 5 workflows present after installation of MOSS: Approval, Collect Feedback, Collect Signatures, Disposition Approval, Translation Management.
v Sharepoint Designer: This graphical design allows you to create different actions. This can be used by web designers, there's no need to posses any .Net knowledge.
v VS 2005: The possibilities in VS 2005 are huge. You can accomplish almost everything, but it has to be developed. These workflows are usable throughout the entire portal. When it is not possible with Sharepoint designer, we have to use VS .net 2005. You'll need in dept .Net and VS2005 knowledge to create workflows.
Comparing Workflow Development Processes
The figure below illustrates the various steps that need to be performed to create, deploy, associate, and run a workflow using each of the authoring tools. In general, the largest difference between the two tools is this:
v Workflow authoring in the Visual Studio 2005 Designer for Windows Workflow Foundation is performed by a professional developer, who is creating a workflow template that can be deployed across multiple sites, and contains custom code and activities. The developer then turns the workflow template over to a server administrator for actual deployment and association.
v Workflow authoring in Office SharePoint Designer 2007 is done by someone other than a professional developer, such as a web designer or knowledge worker, who wants to create a workflow for a specific list or document library. In this case, the designer is limited to the workflow activities on their ‘safe list’, and the workflow cannot include custom code. The workflow author deploys the workflow template directly to the list or document library as part of the workflow authoring process.
For a more detailed comparison of the capabilities and advantages of each tool, see Workflow Development Tools Comparison.