You simply cannot run multiple instances of a workflow on the same item - at least not if it's a list-item workflow. You would need to create a site-workflow to have multiple concurrent instances.

Hi,

as previously said, you cannot run several instances of the same list workflow version on the same item, but of course you can start a Site Workflow using web services..have a look to StartWorkflow method in weburl/_vti_bin/nintexworkflow/workflow.asmx

Giacomo

Thanks you're so right. The direction I need to go is to execute a Site Workflow from Web Services within the List Workflow.

Yes I need to execute a site workflow from web services.