"Unable to instantiate observers" !!??

Hi,
When I run ‘rake db:migrate’, I get this error message:
“Unable to instantiate observers, some gems that this application depends on are missing. Run ‘rake gems:install’”>

When I run ‘rake gems:install’ as the error message suggests I get the very same above error !!

I googled the error message but I didn’t find any help …
Any idea??