Hi Alex,
I believe the problem lies with Ch61to75.html. When I open the epub file with 7zip it shows that this file has an unpacked size of 301338 bytes and a packed size of 116138 bytes. I'm no expert, but I believe the Sony reader has a limitation of 300k uncompressed and 100k compressed. Maybe and ADE or epub standard limitation?
When I split Ch61to75.html at chapter 71 the book works correctly on my Sony PRS-650. Doing this gave me file sizes of:
Ch61to70.html: 211853 bytes uncompressed, 80932 bytes compressed
Ch71to75.html: 86001 bytes uncompressed, 33635 bytes compressed
Hope this helps