I received this error when building an interaction model after manually batch adding many sample utterances to an intent. I solved the error two times:1) Changed the word "CDs" to "cds"2) Slowly added all sample utterances from the batch (saving and building between each addition of a few utterances).
This error was in no way related to the fix and there was nothing pointing me to the utterances that needed to be changed.
Source: amazon.com