The line giving you problems there is
[p pluginname e v] = fileparts(pluginfiles(k).name);
notice that there are four outputs there. That had to do with the file name structure on the DEC VMS operating system, which has not been supported by MATLAB for many years.
Go through the code, and in any call to fileparts that has four outputs, delete the last output. If you need to, you can set that variable name to '' (the empty string.) For example,
[p pluginname e] = fileparts(pluginfiles(k).name);
v = '';
There might be other changes needed. SPM8 is not entirely compatible with SPM5.