It now works through the calculation stage nicely. I get a partially completed seqences printed into Analysis main window. Then it tries to do next step and fails with this traceback: Done typing spin systems Exception in Tkinter callback Traceback (most recent call last): File "/usr/lib/python2.4/lib-tk/Tkinter.py", line 1345, in __call__ return self.func(*args) File "/usr/lib/python2.4/lib-tk/Tkinter.py", line 456, in callit func(*args) File "/usr/local/ccpnmr1.0.9/ccpnmr1.0/python/ccpnmr/analysis/SpinSystemTypingPopup.py", line 724, in updateSpinSystems typesText = ' '.join(spinSystem.sstTypes) TypeError: sequence item 0: expected string, NoneType found Cheers Krys -- Dr. Krystyna Bromek === Biomolecular NMR ==== University of Glasgow, IBLS Joseph Black Building B4-17, Glasgow G12 8QQ, UK Tel: 0141 330 6551/6459