After installing Sitecore v6, you get the following error when viewing the website or sitecore UI:

Sitecore Could not load file or assembly ‘System.Data.SQLite, Version=1.0.48.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139’ or one of its dependencies. An attempt was made to load a program with an incorrect format.

This is actually detailed in page 20 of the sitecore troubleshooting doc, but I missed it first time round. This is caused by the presence of System.Data.SqlLite in the bin folder when running on 64-bit OS. An alternative dll is available for 64bit OS from Sitecore.

Solution: If you’re are not using SQLite simply the delete the System.Data.SqlLite.dll from the bin folder and recycle your app to get back up and running. If you are using SQLite, download the alternative dll for 64bit OS.