Just down-loaded the sheet in your link, and it is different than the one I got from Maxim's site on March 19 of this year.

The "I2C" vs "serial" wording I think was just due to some patent / copyright issues.

Since the 1307's register map only goes to $3F, writing a WORD for the register address probably causes problems. Use a BYTE instead - works for me!

Arch