I recently updated the Blog Templates plugin on a multisite network and since then, if I try to create a new site I get a white screen when clicking "Add Site".
The site is created but no information is copied from the templated site.
I haven't tried deactiaving all the plugins, etc. As I said, this seems to be related to the 2.6.1 upgrade. The only other plugin in my system that was recently updated in the Post Indexer, which your team also creates and supports.