When connecting to Novell eDirectory and modifying the schema an "Attribute Or Value Exists" error occurs. This is due to the modification performing an add before the delete and eDirectory (wrongly) complains that the same OID has been used more than once before realising that the old value should be deleted. Note that this is a problem with eDirectory but it would be useful if Studio asked for the delete to be performed before the add when modifying an attribute value which eDirectory is OK with.
An example of the LDIF in the modifications logs view for an operation that fails is:
objectClasses: ( 2.16.840.1.113722.214.171.124 NAME 'inetOrgPerson' [...new value...]
objectClasses: ( 2.16.840.1.1137126.96.36.199 NAME 'inetOrgPerson' [...old value...]
It also seems that modifying the schema on ApacheDS has the same issue.