@mpompolas @MartinC
Could you please share an example of the files you used to write the functions in_fopen_nwb.m/in_fread_nwb.m?
What is currently in Brainstorm can't be used for generic EEG files, it seems extremely specific to one dataset: eg. it needs to have one and only one recorded signal set named "raw" OR one and only processed signal set named "lfp".