at least one resource should be selected
then when i deleted the folder and tried to commit the deletion instead (not knowing it wasn't in svn at all) i got the following message:
Some of selected resources were not added to version control.
Some of selected resources were not committed.
svn: Can't add '/home/me/workspaceJuno/projectB/testfolder/testfile.txt' to a parent directory scheduled for deletion
svn: Working copy '/home/me/workspaceJuno/projectB/testfolder' locked
i finally figured out that the problem was that when i copy/pasted the testfolder inside eclipse, from Project A to Project B, it had copied the .svn folder inside testfolder as well, so eclipse thought it was already in svn in Project B. so when you copy folders inside eclipse from one project to another, you need to manually delete the .svn folder in a normal file browser, e.g. nautilus, then you will be able to commit the folder.