I had tried the -f option earlier as part of fetching of fetching the command line from test runner option. Had even tried changing it from default workspace to other directory; but it does not seem to find the required and still complains the same
Couple of points - were you able to see the reports when it was showing warning? - there is no relationship between workspace and executing the project command line. - do you need to save reports into a customised directory only? - were you able to change the reports directory from the tool? And are then reports generated? - if so, you can use launch testrunner from ui and note down the command and use that directly next time in command line.