I have installed Post Indexer on our Wordpress multisite,

I have installed Post Indexer on our Wordpress multisite, but it isn't indexing. It keeps hanging on:
6 Sites in queue
6 Sites currently being processed

Can you help me debug it? I have enabled the PI_DEBUG option and I see that it is doing something, however it doesn't index the posts.
I have followed all steps in documentation, but still no progress.