Some kind of data constraint on that column most likely. I've seen this when the field was created with the default size for text fields, instead of our recommended size of 2000. In some networks, the size of this field might even need to be larger to accommodate the entire circuit graph.
I would verify the size of the CIRCUITGRAPH field in the database; if that's not the problem, I can take a more detailed look into this if you can submit a support ticket on the problem. Let me know if you need any help in getting set up to do that.