Hello Fong,
A damaged index will also cause a large number of errors. The rebuild function fixes the problem. You should run the integrity check again to make sure that the dataset is "clean" before working with it again.
Having a problem like this may occur due to bad power, operator error, a bad network card or network router. A single occurrance can be written off to "act of Windows". Multiple frequent occurrances point to a hardware problem.
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Andrew Bates