(sudo gainroot not working) This surely happens if rootfs fills (because of big growing logs or any other reason). There may be other reasons, but take care the former doesn't happen, make sure you have always free space.
(installer) Please elaborate a bit more. Is it an issue with the installer script? Please post one of such messages and your module's directory listing if so. The script doesn't expect to find all installed modules in kbuilds/foo, it just looks for those existing in kbuilds/foo to replace the installed ones under /lib/modules/2.6.21-omap1.
I haven't had any issue with wifi. Is the AP open, WEP or WPA?