WU-ftpd configuration problems (was: 553 Could not determine pwd ir: No such file or directory.)

Now it's become urgent --- Dear all, after creating a chrooted environment for a non-anonymous user with WU-ftpd 2.6.1, I get the following error message when trying to upload files: --- 200 PORT command successful. 553 Could not determine pwdir: No such file or directory. --- Dowloads work fine though. Any clues? Maybe I'm overseeing something obvious... Thanks in advance! Martin