I'm a newbie and my snake took about four weeks to get from eating live to frozen/thawed.

I kind of suspect the time was what did it, but it was also the first time I accidentally over warmed the rat, so it was basically boiled. Snake struck and constricted, and the rat exploded.

Yum. Snake enjoyed its meal, though I really have to say the smell of parboiled rat intestines is not particularly appealing.