unable edit existing log message

Hi,

I have been trying to edit the already existing log message using
TortoiseSVN tool but it is giving me the following error. I can see that the
file pre-revprop-change hook exists in hook scripts folder with .tmpl
extension and it is executable.
*
*
*DAV request failed; it's possible that the repository's pre-revprop-change
hook is either failed or is non-existent*
*At least one property change failed; repository is unchanged*
*Error setting property 'log':*
*Repository has not been enabled to accept revision propchanges;ask the
administrator to create a pre-revprop-change hook*

Version of SVN: *1.4.6 (r28521)*

-- 
Thanks,