Upgrading Joomla 1.5 site to 2.5 using jUpgrade unique article alias issue-Collection of common programming errors

I am trying to upgrade my Joomla 1.5.26 site to Joomla 2.5 using jUpgrade 2.5. During the update process jUpgrade gets stuck on Migrating undefined.

After enabling the debug, the error shown is

JLIB_DATABASE_ERROR_ARTICLE_UNIQUE_ALIAS

Is there a way to prevent this unique article alias error?

Screenshot below