Hi, While assigning a peak the following error occured. ">>> Exception in Tkinter callback Traceback (most recent call last): File "/home/karthik/ccpnmr.new/ccpnmr/python2.4/lib/python2.4/lib-tk/Tkinter.p y", line 1345, in __call__ return self.func(*args) File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/memops/gui/ScrolledMatr ix.py", line 605, in mouseClick self.selectCell(row,col) File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/memops/gui/ScrolledMatr ix.py", line 1597, in selectCell self.callback(self.currentObject, objRow, objCol) File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/ccpnmr/analysis/BrowseA tomsPopup.py", line 622, in selectCell assignmentPanel.chooseAtoms( object ) File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/ccpnmr/analysis/EditAss ignmentPopup.py", line 690, in chooseAtoms self.assign(atomSetMapping) File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/ccpnmr/analysis/EditAss ignmentPopup.py", line 618, in assign if (not atomSets0) or self.checkBmrbShift(resonance, atomSets0[0], self.peak Dim): File "/home/karthik/ccpnmr.new/ccpnmr/ccpnmr1.0/python/ccpnmr/analysis/EditAss ignmentPopup.py", line 650, in checkBmrbShift typeScore = getAtomProbability(chemAtomNmrRef, shift.value) AttributeError: 'NoneType' object has no attribute 'value' >>> The assignment panel opens fine and on clicking the assign button the atom browser opens properly as well. But on clicking on an atom to assign, this error message is displayed and the assignment is not made. Karthik I have been using this version (11) for a while and have not encountered such an error before.