This YSOD error drove me batty for a few hours, simple resolution though.

Could not load file or assembly 'System.Data.SQLite' or one of its dependencies. An attempt was made to load a program with an incorrect format.

You'll experience it with Sitefinity when you setup a new site in IIS.  By default "Enable 32-Bit Applications" in the App Pool settings for the new site are "FALSE"...turn it to "TRUE" and it'll all work fine again (*sigh*)

**Update Dec 28th, 2012**
That assembly doesn't appear to be required, just kill it from the bin folder and you don't need to run in 32-bit more anymore.

Cheers