Unable to start ADMIN web interface

Hi folks

We have a test LPAR that I'm using to check that applications at V5R2
will work okay at V5R4. As part of that I am trying to get iSeries
Access for Web configured, but I'm falling at the first hurdle.
Running STRTCPSVR SERVER(*HTTP) HTTPSVR(*ADMIN) results in a HTP8001 -
HTTP Server instance ADMIN start up failed. The details in the ADMIN
joblog give a little more info:

HTP8005    Diagnostic
 Message . . . . :   Directive syntax error occurred.
 Cause . . . . . :   The syntax for directive RewriteRule is not correct.

HTP8008    Escape
Cause . . . . . :   HTTP Server instance ADMIN failed because of a
  configuration error on line 22  in configuration file
  /QIBM/ProdData/HTTPA/admin/conf/admin-ibm.conf.

Line 22 is:
RewriteRule ^/QIBM/HTTPSVR/Admin/qzhafrnt.ndm/frontpage$ /HTTPAdmin [R]

The configuration file is nearly identical to those on other
partitions (V5R4 has additions for using Eclipse Help & WAS at the end
of the file but otherwise matches line for line), where ADMIN works
fine, so I'm wondering if there is some other issue that's causing
this.

According to the IBM web server FAQs
http://www-03.ibm.com/servers/eserver/iseries/software/http/services/faq.html#Versions
we have all the prerequisites, but the troubleshooting sections in
info center don't list this problem.

I did find someone with just the same problem (and moving off an 825
at V5R2 too) via Google
http://www.tek-tips.com/viewthread.cfm?qid=1265640&page=1 but no
solution has been posted :(

The usual checks on authorities and on the QTMHHTP1 & QTMHHTTP
profiles haven't shown up anything - so where next?

Regards, Martin