some more data…
i can produce 1 (one) test per class. usually, it is the first method, when i request tests for all methods in the class. when i request a test just for method 5, i get one test for method 5. further single requests are ignored (with that error-msg). when i delete the generated testfile, i can get another test for another method.
when everything worked, diffblue often generated more than one junit test per method, here i get just one.
it seems, the problem is writing the generated tests into a non-empty file.