You need some root enabling package like rootsh, sudser, opensshor the like installed to correct this error.
If you do not have any of these installed, you might just go and try to make a backup of your settings and contacts and stuff and reflash.
Then you might closely look at the memory space on rootfs, /home, MyDocs and swap. Some might be corrupted. But again you need some root enabling packages for this to work out.