The ability to read Erdas Imagine files is not available in MATLAB. The MULTIBANDREAD function reads raw, uncompressed binary data stored in one of three simple configurations. It does not support the Erdas Imagine (.IMG) format.
As a workaround, convert the file from Erdas Imagine .IMG format into a format that IMREAD accepts. This conversion will need to be performed in another application. A list of these formats is available in the documentation for IMREAD which is available by typing "doc imread" at the MATLAB command prompt.