State machine workflow not getting associated with content type

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SharePoint

Hi,

I am deploying my workflow on custom list. this workflow runs on custom content type which is inheritaing from windows task content type.

but when I am trying to run this workflow it is showing error , till add & I run Sharepoing inbuild workflow. like approval or something else workflow.

why my workflow is dependent on sharepoint in-build workflow. ??

Help please.
tx
shrimali