Workflow Soluiton

I'm testing out my workflow project and after using workflowmanagement to clear out any old tasks/processes, I go to http://servername/projectname/composer.aspx?StartWorkflow=true and I get this error:

"only one task is allowed to be created when starting workflow in the dialog workflow mode"

what's going on?

Not sure without seeing your workflow.  But it sounds like you are splitting your paths to two different dialog workflows on startup.  (Are you using advanced workflow?)  You can only have 1 form be the startup I think.
Could you post a screen shot of your project? 

Support did not find the actual details of the problem, but they asked whether I had copied dialog workflow components within the model, and I had, which apparently is a really bad idea. I re-created all of the dialog workflow components and it is now working correctly.

I have the same problem with one of my projects. Did you totally have to recreate everything from scratch or were you able to simply drag a new Dialog Workflow component into the model, copy the components from the Dialog Model (under the "Interaction Setup" tab) of the offending copy/pasted Dialog Workflow component into the new one and then delete the old one?

Yes, just create a new one, go into the interaction setup (and/or event configuration) and copy the components inside, then open the same section of the new dialog workflow and paste.  Then delete the old one.  It worked like a charm for me.