A few bits to this problem:
I am trying to set up my Axon Mote with a DS1307 RTC.
I tried using the latest Webbotlib Studio; After adding an I2C Master, selecting the DS1307 from the devices dropdown doesn't do anything. Some of the devices in the list work, but some others also don't (a partial sampling, I found that the TPA81 and Devantech CMPS03 (I2C) Compass both fail).
(Also, even fewer devices are valid selections if I try using my custom Attiny85 .brd file)
I went back to Project Designer; I can add the RTC to the I2C Master, but am unable to choose anything for or bypass the Supply Vcc. I suspect this may be the issue that Webbotlib Studio is hiding from the user? This seems very similar to an issue I had a couple years ago that you fixed: http://www.societyofrobots.com/robotforum/index.php?topic=14465.0
Both programs work fine if I use a regular Axon, so I'll use that in the mean time.