Хорошая начальная точка, должен посмотреть на файл журнала запланированной задачи, поскольку он даст Вам более подробный журнал. http://support.microsoft.com/kb/308558
Try this:
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
...
RewriteCond %{REQUEST_URI} !(.*)/$
RewriteRule ^(.*)$ $1/ [R=301,L]
You can add your exceptions where I wrote ...
and it will redirect only if there is not already a trailing slash.
EDIT:
found this and verified that it works:
RewriteCond %{HTTP_HOST} !=""
RewriteCond %{THE_REQUEST} ^[A-Z]+\s//+(.*)\sHTTP/[0-9.]+$ [OR]
RewriteCond %{THE_REQUEST} ^[A-Z]+\s(.*/)/+\sHTTP/[0-9.]+$
RewriteRule .* http://%{HTTP_HOST}/%1 [R=301,L]
This should do what you are trying...