mini versus pro mini with SHT15

I am having problems getting the SHT15 to communicate with a pro mini 5v. All the code works with the mini but not the pro mini. I have tried a few examples using code off the web:

http://www.flatline.net/journal/2008/04/11/arduino-reading-the-sht15-temperaturehumidity-sensor/

  • returns limits (h: 0 and temp: -40) implying no communication
  • hangs

http://www.glacialwanderer.com/hobbyrobotics/?p=5

  • returns ACK error 1

Has anyone had similar difficulties? solutions?

thanks, don