For example, I tried installing Gimp on /mnt/card, when I try to launch it i get an error msg saying it can't find libgimpwidgets-2.0.so.0....
Try uninstalling all those programs [which fails to run] then re-install them one at a time, and after each one check the
log tab of the package manager. Or just use
ipkg-install and
ipkg-uninstall from the command line so you can see whether any error messages come up.
In case you didn't know, after installing any package to external storage, the installation process (either the package manager or ipkg-install runs
ipkg-link. This creates symlinks in / which points to the newly installed files (ie in your case /mnt/card). My guess is that for some reason those symlinks aren't being created properly, that is why you need to check the
log tab of the package manager.
-- cheers