StaticGround

If you ever get this error when undeploying a pipeline or schema assembly in BizTalk 2004:

Some items in the removed assembly are still being used by items not
defined in the same assembly, thus removal of the assembly failed.
Make sure that items in the assembly you are trying to remove fulfill the
following conditions:

1. Pipelines, maps, and schemas are not being used by Send Ports or Receive
Locations
2. Roles have no enlisted parties.

Try the following:

Don't forget to write down what the current settings are, once you've undeployed and redeployed the assemblies, you'll need to update the settings that you changed to their original values.

* Change the send ports send pipeline in the Visual Studio BizTalk Explorer (Edit | Configuration | Send | General) to reference the default Microsoft.BizTalk.DefaultPipelines.PassThru
* Remove all outbound maps that are associated with the send port in the Visual Studio BizTalk Explorer (Edit | Configuration | Filters & Maps | Outbound Maps)
* Check that your roles do not have enlisted parties.

doing these steps should allow you to undeploy the assemblies.