My library is on a different drive (a Windows drive), rather than the main LInux drive. Guayadeque 0.3.5 recently lost the library. I tried to set it up again so that it would rescan on startup. I made sure the Windows drive was mounted first. It still isn't updating. I've read elsewhere here that a possible solution might be to rescan the library -- but I can't find the command for that, nor can I find it in the documentation. I really *love* Guayadeque's smart-playlist feature, much more powerful and predictive than iTunes or Songbird.
In the screenshot you will see the cursor hovering 'Update' and on the left the name of the collection you would either update or rescan(directly below update), in this case the collection is 'NEW'.
In the case you don't see the collection you wish to rescan/update, if you look directly to the left of Update in the screenshot, you will see a collection called 'MUSIC' which by clicking will allow you to activate the MUSIC collection. The MUSIC collection would then be visible at the top with the All_Music and NEW collections, with the submenu allowing you to Update/Rescan.
It may be that you somehow chose the 'Show' option which deactivated the collection you're having problems with. Hope this helps!