Hi, I find that the "Find peak" button on a Peak Selection popup also offers windows that are in an inactive window group and gives the traceback below: Exception in Tkinter callback Traceback (most recent call last): File "/usr/lib64/python2.2/lib-tk/Tkinter.py", line 1316, in __call__ return apply(self.func, args) File "/usr/local/ccpnmr/ccpnmr1.0/python/ccpnmr/analysis/SelectedPeaksPopup.py", line 311, in findPeak popup.gotoPeak(self.peak) AttributeError: 'NoneType' object has no attribute 'gotoPeak' I guess inactive windows should just not appear in the list? -- Dr. Brian O. Smith ---------------------- B Smith at bio gla ac uk Division of Biochemistry & Molecular Biology, Institute Biomedical & Life Sciences, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK. Tel: 0141 330 5167/6459/3089 Fax: 0141 330 8640