Why reducing data frequency causes segmentation fault？

[lenninghuiliu]

word_freq = { "2001": 1, "pst": 1, "2000": 1, "call": 1, "thu": 1, "question": 1, "follow": 1, "regard": 1, "contact": 1, "energi": 1, "current": 1, "legal": 1, "problem": 1, "industri": 1, "transport": 1, "target": 1, "exactli": 1, "enterpris": 1 }I changed word_freq to this and generated the data set using python. Appears when running ROSE program Segmentation fault