I2C LCD + DS1307 , work separately but not when I share the Bus

Thank you for the help John.
http://web4robot.com/LCDCtrl.html is the controller.
In the manual it does say:
"I2C Slave Interface : Industry standard Philips I2C bus compatible interface.
Data rate 100 kbps. "

A little more testing shows that the LCD operates OK on the I2C bus with both hooked up, but the clock always returns 0:0:0 when I write the time to the LCD.
When I have both hooked up but run code that ONLY read/write to the RTC and shows results via serial back to the PC I get mixed results of 0:0:0 and sometimes random times.

Is there a better i2c controller I should buy for my LCD ?
I may be able to sacrifice two more I/O pins and just run it serial .. but would prefer not to.

Thanks !