Please report MODELLER bugs by e-mail to the MODELLER developers (for contact information, see http://salilab.org/modeller/contact.html), or, if you suspect your inputs may be faulty (and the files are not confidential) to the users' mailing list (see the same web page).
In order to be able to reproduce the bug, we will need all of your original input files (e.g., script file, alignment, PDBs). In most cases, the full output demonstrating the error(s) you receive is useful too.
Please do not paste your input files directly into your email, but instead put them in a .zip or .tar.gz file. That way, we can see the exact same files you're using.