problem with Picasa, when switching users

[Boo]

It looks like you may not need both devices.

you could test this (or just provide more info) by listing them in both user accounts.
login as you and run:
ls -l /dev/nvidia*

login as your fiance and run:
ls -l /dev/nvidia*

there could be some other permission problem or config error for your account not to work but it just shows up with the one you listed.

[Boo]

yes it is permissons.
they are set to 660 for both devices.
and like the error suggested you have to set them to 666.

looks like you did not use a sudo on the chmod or if you look carefully the last letter of the second device is a "l" (lower case L)and not the number "1" (one), and since the device with a 1 at the end does not exist the command fails.
run:
sudo chmod 666 /dev/nvidia0
sudo chmod 666 /dev/nvidiactl


BTW i use f-spot as my photo/camera tool of choice.