My Object data source was looking in my ProcessBSL for a method called ProcessDelete with the corresponding signature. I had written my methods in the code behind ProcessBSL file.
This was the line of code that effected it:
TypeName="DataWarehouseUserInterface.ProcessBSL"
Summary: If it's throwing this error for you, ensure your method signature is correct. Ensure that the BSL layer is correct. Make sure you have _ - that also stopped mine from working. Hope this helps someone else.
Cheers.