On requesting to join, using a gmail account, I get:
"You do not have permission to join this forum"
Anyone should be able to join -- I just tested this with another email address, and there are indeed a few people on the list now. If you are still having issues, send me your email and I'll add you.
Because there are a significant number of people attempting polyphasic sleep simultaneously, I figured that it would be high-value to create a Google group / mailing list for those who are trying it and would like emotional support, advice, and encouragement. This is for sharing your experiences, techniques to fall asleep or wake up, questions about whether your response is typical, etc. Knowing that there are other people out there trying the same thing helps one stay the course -- especially in the middle of the night, when the people around you are probably sleeping.
https://groups.google.com/forum/#!forum/polyphasic-support