It spend me so long time to get this problem solved.
1. I found a blog, it just says: to check the log. ok, then I go to check the log. Found it says my "Shared Services Provider" doesn't work.
2. I go to admin, create a new SSP, but it complains provision does not work, go to check log again. Found it says somebody else me is the site owner.
3. Go to command line, type stsadm -o siteowner to change it to myself. Now it complains some parameter does not work.
4. Found an article saying to add the app pool id into site admin, but it already there.
5. So I type in the below command to force my account be the farm admin: C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm -o updatefarmcredentials -userlogin ds\sseadmin -password password, then try again.
6. It worked!
Now if you can not start your workflow, please post comment here, and I will try my best to answer your question.