The bug:
 
The bug in DotNetNuke is where a scheduled task that synchronizes the file system (on the web host with what is registered in the database) fails to successfully access the files. Once it does that it records back in the database to delete any records from files that it can't find. Any kind of hiccup on the web host could cause this to happen. Once it deletes the file references the RSS looses the reference to the style sheet. The reference is still in the ModuleSettings table (settingname of "xslsrc"). This may affect other modules as well. A secondary bug in found at DotNetNuke.com where I can't seem to easliy find a bug report, a support section, or related content in the forums. This post addresses both bugs. :)
 
The fix:
 
I reset the file permissions to allow everyone to view the files and re-synchronized the file system with the database. I then turned off the synchronization in the Host --> Schedule menu (not necessary anyway in most cases...as far as I can tell). I also updated the module settings through the database with a SQL query and saved it in case this ever happens again...which it won't unless that schedule is re-enabled.