I have a managed package that works for 99% of installers, but 2 are returning these email errors to me:

Apex script unhandled exception by user/organization: 00560000000nYMJ/00D30000000039c

Failed to invoke future method 'public static void evaluateLeads(SET:Id)'

caused by: System.NullPointerException: Attempt to de-reference a null object

(leadScoring)


External entry point

Debug Log:

This trigger calls a bigger class, which should exist upon install unless something went wrong:

trigger evaluateLeadScoringRulesLeadInsertOrUpdate on Lead (After insert, After update) {

    Set<Id> leadIds=new Set<Id>();

    //Needed as asynch apex does not allow passage of Sobjects, only Set's
    for (Lead l:trigger.new){
        leadIds.add(l.Id);
    }//for

    //Send that list of created or updated campaign members to the apex class for processing
    system.debug('Future lead scoring method evaluateLeads already called? '+LeadScoring.leadScoringClassAlreadyCalled());
    if (LeadScoring.leadScoringClassAlreadyCalled()==False){
        system.debug('# Future Calls until limit hit: '+Limits.getLimitFutureCalls());
        if (Limits.getLimitFutureCalls()>0){//don't call the method if the limit is reached
            LeadScoring.evaluateLeads(leadIds);    
        }    
    }    
}//trigger

Class called from the trigger that seems to be the source of the NPE:

public global class LeadScoring {

    public static Boolean leadScoringClassAlreadyCalled=FALSE;

    public static boolean leadScoringClassAlreadyCalled(){
        return leadScoringClassAlreadyCalled;
    }

    @future //this method is called from the trigger.  It's an asynch method so the trigger call has high governor limits
    public static void evaluateLeads(Set<Id> leadIds){
        evaluateLeads2(leadIds);
    }//evaluateLeads    
    
    //this method is called from batch apex.  It cannot be an asynch method as batch apex can't call @future methods
    public static void evaluateLeads2(Set<Id> leadIds){
        Integer i,j;
        Double scoreChange;//safer to define as a double in case anyone tries to change the field's # decimals
        Schema.DescribeFieldResult cmFieldDescribe;
        leadScoringClassAlreadyCalled=TRUE;
...
...

Could these be caused by:

1. No apex perms for the running user?
2. Bad package install?
3. No @future perms for the running user?