error message -- March 14, 2014 - 16:48

Hello,
I keep having the following error. I looked into the mailing list and I think 
I cleaned up the spin container in order to keep only the spins that are 
contained in the text files originated from Bruker Dynamics Center.
ANy hint for help?
Thanks,
Stefano

Traceback (most recent call last):
  File "gui/analyses/auto_model_free.pyc", line 588, in execute
  File "gui/analyses/auto_model_free.pyc", line 416, in assemble_data
AttributeError: 'SpinContainer' object has no attribute 'isotope'