Problem adding new Admins post SP1 rollup4

[Rexif]

After upgrading to Exchange 2007 SP1 rollup4 (from 2007 RTM) I am not
able to give administrator rights by using the GUI or the management
shell. I get the following error:

==========
Active Directory operation failed on DC.<root>.com. This error is not
retriable.
Additional information: the specified user does not exist.
Active directory response: 00000525: NameErr: DSID-031A0F80, problem
2001 (NO_OBJECT), data 0, best match of: []"

The object does not exist.

Exchange Management Shell command attempted:
Add-ExchangeAdministrator -Identity '<child>.<root>.com/OU/OU/User" -
Role RecipientAdmin
==========

There is a GC in the Root Domain.
Setup.com /PrepareAD was successfully run in the Root
Setup.com /PrepareDomain: <child>.<root>.com was successfully run from
the root

No errors in the setup logs.

I've found 1 post that has the same error.
http://forums.msexchange.org/m_1800465347/mpage_1/key_/tm.htm#1800465347

Trying Setup.com /PrepareDomain and Setup.com /PrepareDomain:
<child>.<root>.com did not fix. (should be same as running all
domains?)

Any ideas would be helpful.

I've checked replmon between domains and GC's, its good.
I've checked schema version in ADSIEdit

I can add users manually to the Exchange admin groups, but this does
give me a warm fuzzy about the environment.

This worked with the RTM version.

[Rexif]

The user does exist ;)

[Rexif]

The above post was only to indicate I checked the obvious, not to
suggest the problem was solved.