The error message I'm getting is:

I could not find the relation Resources in ResearchGroupPage or any of its ancestors.

The problem seems to be coming from section of code starting at line 29 in ManyManyDataObjectManager.php
foreach($classes as $class) {
if($class != "Object") {

Here's the relevant code from my DataObjectAsPage files:

----

class ResourceItem extends DataObjectAsPage {
//The class of the page which will list this DataObject
static $listing_class = 'ResourcePage';
//Class Naming (optional but recommended)
static $plural_name = 'ResourceItems';
static $singular_name = 'ResourceItem';

public static $db = array(
'Date' => 'SS_Datetime',
'PublicAccess' => 'Boolean',
'Directory' => 'Text',
'URI' => 'Text',
'ResourceType' => "Enum(array('Web', 'File'), 'Web')",
);

public static $has_one = array(
'Owner' => 'Member',
'ResourceFile' => 'File'
);

public static $many_many = array(
'Tags' => 'Tag',
);

public static $belongs_many_many = array (
'ResearchGroups' => 'ResearchGroup'
);

------

class ResearchGroup extends DataObjectAsPage {
//The class of the page which will list this DataObject
static $listing_class = 'ResearchGroupPage';
//Class Naming (optional but recommended)
static $plural_name = 'ResearchGroups';
static $singular_name = 'ResearchGroup';

public static $has_one = array(
'Creator' => 'Member'
);

public static $many_many = array(
'Members' => 'Member',
'Resources' => 'ResourceItem',
'Journals' => 'JournalEntry',
'Publications' => 'Publication'
);
.......

class ResearchGroupPage extends DataObjectAsPageHolder {

}

class ResearchGroupPage_Controller extends DataObjectAsPageHolder_Controller {

// Here's the relevant part of the form I'm trying to display on the edit page for a Research Group

function ResearchGroupForm() {
// Must be logged in
$member = MEMBER::CurrentMember();
if (!$member) {
return Security::permissionFailure($this);
}

//Create form fields
$fields = new FieldSet (
new HiddenField("ID", "ID"),
new HiddenField("CreatorID", "CreatorID"),
new TextField('Title', 'Title'),
new HTMLEditorField('Content', 'Description'),
$resources = new ManyManyDataObjectManager (
$this, // Controller
'Resources', // Source name
'ResourceItem', // Source class
array(
'Title' => 'Title',
'Content' => 'Content'
),
'getCMSFields'
)
);

---------------------------------

Thanks, Shelly