Re-activating an old website on IIS the browser showed HTTP Error 503.
More fully the error given within the browser was:
HTTP Error 503. The Service is Unavailable
The website was a development site which had been stopped and was now to be re-activated.
Reviewing the IIS settings for the website, nothing looked to be wrong. It was running.
A review of the assigned application pool showed this to have also been stopped , at the time the website was taken off-line.
This error was caused by the application pool not being enabled in IIS.
In IIS click on the Application Pools menu item in the left hand tree menu to show a list of the Application Pools.
If the application pool is stopped, click on its line item and then in the right column click on Start.
