Why are my roll-overs not working?

Dear People,
I have two web pages that use roll over buttons at the bottom of each page.
Unfortunately, the second image of each button, the one that should appear
when my cursor is over it, does not appear. Instead I receive a blank
rectangle with the little pink x in the upper left corner.
Can you look at my code and tell me what is going wrong? The pages work fine
on my computer.
The web site is at http://www.familyshoebox.com/family/PaleYellowCat
The pages in question are The First Day and The First Day Part Two. I would
be grateful for any help!
Thanks!
Michael Guadagnino

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