Membership PayPal Plugin - Error Invalid Regular period

Not sure right off as I haven't tried it but Andrew and crew aren't supporting wp3 until it gets officially released. There may be an answer but I did want to point that out.

https://premium.wpmudev.org/blog/wordpress-3-0-and-wpmu-dev/

I;m supposed to point you at the Compatible With box along the right hand side of this page:

https://premium.wpmudev.org/project/membership

Hopefully though someone has tried it already.