Reporting Services 2005 was installed on a virtual machine prior to a sysprep. I received errors from http://localhost/Reports and http://localhost/ReportServer that ultimately indicated that it couldn’t connect to the reporting database.
The resolution to this is to run a tool called "rsconfig". In my case, which I suspect is pretty common, the required command was:
rsconfig -c -s localhost -d ReportServer -a Windows
This led to the next issue, which was that Reporting Services was no longer able to "decrypt the symmetric key used to access sensitive or encrypted data in a report server database". I believe this is due to the fact that the public/private key of the virtual machine was changed after sysprep was run. Better practice (I’ll refrain from using ‘best practice’ here, as I’m sure there is a better process) would be to backup the symmetric key using the Reporting Services Configuration Manager before running sysprep, and then restoring it afterwards.
However, I had not backed up the key. So the solution was to use the configuration manager’s "Delete encrypted content" feature on the "Encryption Keys" page, then "Change" the key. This was fine for me to do as I had no schedules or encrypted connection strings in my Reporting Services database.