Did little testing, and it seem that version 4.3.0 has working Geocaches for N900. In that version I can find the separate Geocaching icon in the menu to turn them on and off. This menu symbol is missing in 4.5.1 version.

In the first post it reads that the Geocaching is supported only on N9, but in the user guide it says it is only supported in the N900 version. Is there a possibility that the menu setting have been messed up between these version and that has somehow disabled the caching in 4.5.1 version in N900. I also noticed that the 4.3.0 version writes additional line to the settings.ini where the filename of caches.db is stored (same name as the database line), but adding this line to the 4.5.1 does not bring the caching to the Mapsi.

Edit: Seem that I have problem also with version 4.4.0.

Well I'm downgrading to 4.3.0 until this problem is solved.