Request Tracker says config file is locked

Symptom: I openrf Request Tracker in my browser and instead of the login screen, it said:

Config file /etc/request-tracker/RT_SiteConfig.pm is locked 

Since I had no idea what the cause could be, I asked Google. All the forum entries it pointed me to said that it's because request-tracker can't access MySQL. But on my system this wasn't the case -- MySQL was running fine.

Checking the logs, I found this intriguing message:

I checked my RT_SiteConfig.pm and, sure enough, I had a trailing slash in the URL. After removing it and restarting Apache, the error went away.

Later, I found that I shouldn't be setting WebBaseURL anyway -- quoting from the RT 4.0 Documentation:

$WebBaseURL, $WebURL

    Usually you don't want to set these options. The only obvious
    reason is if RT is accessible via https protocol on a non standard 
    port, e.g. 'https://rt.example.com:9999'. In all other cases these 
    options are computed using $WebDomain, $WebPort and $WebPath.