Custom Related Lists showing java.lang.NullPointerException

Custom Related Lists showing java.lang.NullPointerException

Is anyone else having problems with their custom related lists? I have two separate lists that have been tested and deployed into production and are suddenly now returning nullPointerExceptions.

These are (or should I say 'were') grabbing information from a remote system and it was returning XML formatted data. The remote system still is reporting XML properly, so I don't have an explanation of why this is happening.