The problem lies with the very first demo under "Neat Examples":
DynamicModule[{text = ""},
Column[{InputField[Dynamic[text], String, ContinuousAction -> True,
FieldHint -> "Enter a string"],
Dynamic[Classify["Language", text, "TopProbabilities"]]}]]
I can reproduce the bug exactly when I evaluate this in v10.0.1 on OSX 10.9.5 (sorry, would have just added this as a comment but am very new here and can't comment yet). I've sent a bug report to Wolfram.
Update. I've heard back from Wolfram. As a temporary fix to avoid triggering the bug, the example can be evaluated properly by adding Classify["Language", "”]
before evaluating the DynamicModule:
Classify["Language", ""];
DynamicModule[{text = "" },
Column[{InputField[Dynamic[text], String, ContinuousAction -> True,
FieldHint -> "Enter a string"],
Dynamic[Classify["Language", text, "TopProbabilities"]]}]]
The remaining "Neat Examples" demos in the Classify docs work without issue.