Thanks for posting back the root cause so others can benefit. The Excel driver built-into SSIS is a 32-bit Jet 4.0 driver which cannot be used in 64-bit mode so your resolution makes a lot of sense. In case you prefer to have all your packages execute in 64-bit mode you can switch your package to use the newer ACE drivers which support accessing Access and Excel 2010 files in 64-bit mode:

Microsoft Access Database Engine 2010 Redistributable (includes ACE OLE DB Driver 12.0)