Believe it or not - it is a rare error and I believe I didn't encounter it yet. As there is not much information about it on the OpenWRT forums, I gathered what I could.
1. Try resetting your device to factory default settings. Usually, this error comes up after installing some kind of dependency or did something that took the whole memory of your RAM.
2. If you're running any services - try disabling them.
3. Try installing the package through the console (if it's opkg). Use opkg install <package path> --force-depends
Hope any of these help you.