iTunes 11 Install Problem "An unknown error occurred (-42110)" - lost all podcasts and music library

Two different things going on at once here.

For the 42110 see the following user tip:

iTunes for Windows 11.0.2.25 and 11.0.2.26: "Unknown error -42110" messages when launching iTunes

For the blank library issue see this post. If you have AVG update it first, if not the techniques given to restore the database still apply, as does the advice to exclude the iTunes library folder from AV scans.

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