"Unable to instantiate observers" !?

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
same above error !!

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