Baking time for paper vs metal
In general, metal is much more thermally conductive than paper (see http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html).  The heat is very likely not making its way through to cook the bottom of your fruitcake as quickly as it would with metal.  I would suggest extending the baking time by about 25%, but also dropping the temperature about halfway through to prevent drying out or burning.

That, or go back to the metal pan that you've had success with in the past.  If it ain't broke...