I am also having this problem. Hakatta, what exactly did you do to resolve?
My setup:
Mac OSX 10.7.2 running Backtrack 5 in Parallels 6
Pineapple Mark IV running version 2.1.0
Swap/usb configured and tested on 4GB usb stick
Everything else seems to work: Karma, urlsnarf, etc. I am able to get sslstrip working on test clients by running it on the Backtrack OS, but not on the pineapple. It does not seem to run at all there, and shuts down the web UI when I attempt to enable it. Issuing a reboot command from SSH brings it back up.