MATLAB R2012a has introduced stricter rules for case-match of features. Since the auxiliary file weatherconv.m depends on three other files - sun.m, irrad.m and irradh.m, and these were written in capital letters (i.e. SUN, IRRAD and IRRADH. ) in the earlier IBPT libraries, the error occurs. Simply re-name the files by using the small letters. The updated files can be dowloaded together with the libraries packages.
Comment July 31, 2012: Unfortunately, it seems that the HAM-Tools models do not run in Matlab 2011b because of the updates made on selector blocks or similar. Any solutions of the problem is highly appreciated! As soon as it is found, the models will be updated.