samba - Jul 2006 - Unable to modify TDB passwd ! Error: Record does not exist

I get this error when trying to set the RID of the Samba administrator 
account (following instructions here: 
http://us2.samba.org/samba/docs/man/Samba-HOWTO-Collection/rights.html#id2580586).

| pdbedit -U S-1-5-21-2442793596-1261311712-3817712761-500 -u 
administrator -r

The full error is:

| Unable to modify TDB passwd ! Error: Record does not exist
|  occured while storing the RID index (RID_000001f4)
| Unable to modify entry!

pdbedit shows the RID as correclty having changed, but I'm then unable to 
change the password for administrator, which gives a similar error:

| Unable to modify TDB passwd ! Error: Record does not exist
|  occured while storing the RID index (RID_000001f4)
| Failed to modify entry for user administrator.
| Failed to modify password entry for user administrator

I'm also unable to delete administrator from smbpasswd (see transcript 
below):

| pdbedit -L administrator
| administrator:1003:Domain_Administrator
| [root@beastie ~]# pdbedit -x administrator
| Unable to delete user administrator
| [root@beastie ~]# pdbedit -x administrator
| user administrator does not exist in the passdb
| [root@beastie ~]# pdbedit -L
| root:0:Charlie &
| [root@beastie ~]# tdbdump /usr/local/private/passdb.tdb
| {
| key(13) = "RID_000003e8\00"
| data(5) = "root\00"
| }
| {
| key(13) = "RID_00000bbe\00"
| data(14) = "administrator\00"
| }
| {
| key(13) = "INFO/version\00"
| data(4) = "\02\00\00\00"
| }
| {
| key(10) = "USER_root\00"
| data(209) = "\00\00\00... [snipped for sanity reasons!]
| }

I found a previous solution to this problem (on this list) which said 
removing/adding the root account to smbpasswd solved the issue.  It doesn't 
in this case.  I can use net rpc rights, as a workaround to this problem, 
but I'd really like to know what gives, if possible?

Many thanks,
Steve :)