Picasa problem - Nikon 4600 - pictures not visible

[Colin Law]

HI

I am hoping that someone has seen a similar problem and can help here.
I have a Nikon Coolpix 4600.  When I connect this to USB on Ubuntu
9.04 or 9.10 (on two PCs) Ubuntu recognises it and an entry appears
under Places labeled NIKON DSC E4600-PTP.  I can open it and manually
download pictures.

If I open Picasa (2.7.0) however (or tell it to open automatically
when the camera is detected - which it does) then the pictures are not
made available for download.  If I click Import, the Select Device
dropdown shows Nikon Coolpix 46000a(PTP mode) as an option, if I
select that it shows it as a title above the Import Tray window but
says there are no files.

Any suggestions will be gratefully received.

Colin