Looks like the indian_pines.hdr ENVI header file has been modified in your system. For a valid ENVI header file, the first four characters must be 'ENVI'.
Use the command below to open the indian-pines.hdr file in the Editor. Then, check whether the first four characters are 'ENVI' or not. If not, you can modify the file to have first four characters as 'ENVI' and, save it.
Then try reading the hyperspectral data with,
hcube = hypercube('indian_pines.dat');