I have seen this type of problem before.
Here are some things to try:
– un-deploy and redeploy the assemblies you are using
– make sure you are not using a custom pipeline, with the Xml Disassembler referencing a single document, and the document is inside the same assembly as the pipeline (if this makes no sense to you then you are not doing it)
– make sure all your maps and pipelines are set correctly after you redeploy
– make sure you are restarting all the hosts (if all else fails try rebooting the computer)
That is all I can think of right now.