Thank you so much @Francois! I'm pretty sure the conflict was due to the presence of EEGLAB in the toolbox folder of MATLAB. I solved the problem moving the EEGLAB folder in another position and removing it from the MATLAB path. EEGLAB includes an older version of FieldTrip lite that could have caused the conflict.
In EEGLAB tutorial is recommended to insert the EEGLAB folder inside the toolbox folder of MATLAB (https://sccn.ucsd.edu/wiki/I.1:_Loading_Data_in_EEGLAB) but this could raise a conflict when using FieldTrip functions on Brainstorm.
Thanks again,
Francesco