The volume bar is shown by a system-ui extension shared library coming from the package system-ui-volume-nokia (/usr/lib/meegotouch/applicationextensions/libsysuid-volume-nokia.so). Most likely the patched system-ui cannot load the library for one reason or another (version mismatch, aegis...). To fix things, get rid of the "unrestricted system-ui" by reinstalling the original ones (as root):

stop xsession/sysuid
apt-get install --reinstall system-ui system-ui-screenlock-nokia system-ui-status-indicator-menu-volume-nokia system-ui-theme-nokia system-ui-volume-nokia systemui-l10n-engineering-english
start xsession/sysuid

In case you get a complaint about not being able to replace a package from a different trusted source/origin, first stop sysuid, then uninstall the modified packages, then apt-get install and start sysuid:

stop xsession/sysuid
dpkg -r --force-all system-ui system-ui-screenlock-nokia system-ui-status-indicator-menu-volume-nokia system-ui-theme-nokia system-ui-volume-nokia systemui-l10n-engineering-english
apt-get install system-ui system-ui-screenlock-nokia system-ui-status-indicator-menu-volume-nokia system-ui-theme-nokia system-ui-volume-nokia systemui-l10n-engineering-english
start xsession/sysuid

(Do understand though that if the device reboots due to a watchdog after dpkg -r you're screwed and need to reflash.)

If you want to understand better why it fails, you can do

stop xsession/sysuid (as root)
sysuid -output-level debug (as user)

and look at the console output.