[Freesurfer] ERROR: could not read header info from T1 or orig

Hi, I have a problem: In the past Freesurfer runs and all go right. Now when I run tksurfer command, a error message appears:

surfer: current subjects dir: models/buckner_data/tutorial_ subjs/group_analysis_tutorial/ surfer: not in "scripts" dir ==> using cwd for session root surfer: session root data dir ($session) set to: surfer: /home/anita/models/buckner_data/tutorial_subjs/group_analysis_tutorial ERROR: could not read header info from T1 or orig in models/buckner_data/tutorial_subjs/group_analysis_tutorial//004/mri

It is strange because the error message appears with tutorial data. Can anybody help me? Thanks, Anita