API Error Code: 191

Filling up the "App on Facebook" page, with Canvas url, ended with / solvet it for me

ex: canvas url.

above issue can be removed via providing the URL for the web site or localhost you are working on, at https://developers.facebook.com/apps/ under Edit-->Website with Facebook Login

Remove the Birthday.aspx from the Canvas URLs.

I was also getting this error when i created a facebook application that was going to be installed onto a tab on a fan page. It turns out that when i first created my facebook application i only filled out the section for "Page Tab" but i didn't fill out the section for "App on Facebook".

i didn't fill out the App on Facebook section because i didn't want users trying to add the app from the app profile page. Anyway, it turns out that by not filling out the App on Facebook section and adding a canvas URL and secure canvas URL i was getting the Error: 191 when trying to make a javascript call to FB.Login().

Once i filled out the App on Facebook section the error went away.