>
> a).  is the xicor X24C16 a 5V +/- 10% part - are you
>     using less than 4.5V:-

The voltage level is within the 10% limit compared to 5V.

>
> b)    are you using the 400kHz I2C mode - the microchip
>     part can be used at 400kHz, the xicor part can't
>     (only 100 kHz mode)

This may be the problem, I'll have to check the clock.

By the way I have grounded the pin 7, I'll check if leaving
that one floating will help.

I already tried using different pull up resistors 10k - 100k
but that had no effect.

Vesku