Increase the maximum number of values for an attribute in Active Directory 2008r2

I have a 2008r2 forest that uses a custom attribute that has reached its limit of values.  Whenever I try to add a new value I get the following error:

Administrative Limit Exceeded (11) Administrative Limit Exceeded
LDAPException: Server Message: 00002024: SvcErr: DSID-0205053D, problem 5008 (ADMIN_LIMIT_EXCEEDED), data -1026

Google provides no insight and DSID-0205053D doesn't seem to appear anywhere.  Any help would be greatly appreciated.

Thanks

Marc