The other day I upgraded my computer, I went from my 6 and a half year old laptop to a 4 year old desktop, and wow that's an impressive upgrade. Anyway, my username changed, hence the path to my photos has changed too, and Digikam stores that info in its internal DB (sqlite). Even if you copy your digicamrc file and your photos, and the digikam4.db database you might have to edit the db yourself to let it know the new path.. This is not as complicated as it may sound.
You can use sqlitebrowser for exampe. On Debian:
apt-get install sqlitebrowser
Then open your digikam4.db (wherever it may be):
and edit the path, "specificPath". Images may help, so voila:
Go to the Browse Data tab, look at the specificData row.
Double click to edit the the cell and correct the value to your new path. Don't forget to "save" the database changes, you should be all set. ... the volume identifier (in my case at least) will be updated by Digikam.
Note: It took about 25 minutes for Digikam to start after these edits, but since it works totally normally.
Hopefully there could/should be a tool in a newer version of Digikam to add a tool to help with this.. Anyway, if this helps you today, that cool. : ]