SSRS Report Manager URL Error “HTTP Error 503. The service is unavailable”

This error is usually caused by SQL Server's Reporting Services sharing either the same port number. In order to resolve this issue please do the following:

1. Click Start --> All Programs --> SQL Server 200* --> Configuration Tools --> Reporting Services Configuration Manager
2. If stopped, click Start on the Report Server.
3. Click on Report Manager URL, and then click the Advanced button.
4. Select the current IP address for Report Manager then click Edit.
5. Change the TCP Port to an available port number that other SSRS services are not running on, then click OK.
6. Click OK, and then Exit.