I have conflict using Polylang 1.0.1 and all in one event calendar 1.9.1 or greater, when using both plugins page permalinks don't work.
Permalink structure /%category%/%postname%/
Calendar page permalink works fine because it doesn't have /lang/ prefix to it however other pages permalinks render 404 error.
Post permalinks however work flawless, I already contacted other plugin support and they redirected me to Polylang support, they only said to try buying premium version of the plugin because:
modification to how the slashes are added to the url that might fix the conflict