Hi Nick,
 
Thank you very much for your reply!
Yes, I have opened the gifti file with freeview successfully.
In matlab, I am using the command:
g=gifti('filename')
with the error message shown before.
I have attached my file that was converted from FS using mri_s:
Also, I have posted a question on the FS support site, but had no reply so far.
Maybe you could have a look at the file. It seems little different
from the template provided at the gifti toolbox homepage.
Best,

Bastian