In this paper, we have reported on epitaxial fully strained La-2/3,Ca1/3MnO3, films grown on single-crystalline SrTiO3 substrates, with thicknesses ranging from 6 to 108 nm. Mn-55 NMR experiments, combined with magnetization data, show that the films have non-homogeneous magnetoelectronic properties and that non-ferromagnetic insulating regions are present close to the interface with the SrTiO3. This observation may account for the repeatedly described disruption of the performance of manganite-based tunneling devices with increasing temperature and may help to better identify the possible causes of the modification of the La2/3Ca1/3MnO3/SrTiO3 interface properties.