if you build a workflow with a BIRT report designed in it, then save the workflow and close it, and then rename the workflow in the workflow explorer, there becomes a problem.
if you now reopen the newly renamed workflow and go to the report designer, it complains about not being able to recall a BIRT designer file, and asks about saving a copy somewhere. If you then make any alterations./additions in the report designer and click save, an error message occurs.
I have seen this error before once or twice, but never been able to track down the root cause. I don't believe it is quite as simple as you describe as I can follow your instructions and it works just fine. Any other potential leads? For example, were the workflows created in an earlier version of KNIME? Also, are you working with MacOS or Windows?
This happens without fail for me using the above process I describe. This is on a 64bit windows 7 pc, and on knime 2.9.4.
Sorry I can't try it on 2.10.1 yet!