[...]
Kernel driver is active, or device is claimed by second instance of librtlsdr.
In the first case, please either detach or blacklist the kernel module
(dvb_usb_rtl28xxu), or enable automatic detaching at compile time.
usb_claim_interface error -6
Failed to open rtlsdr device #0.
Any ideas?
its all there:
the dvb_usb_rtl28xxu kernel driver is active (this is the driver used for watching TV), because ubuntu autoloaded it (probably udevd did)
blacklist it (add: blacklist dvb_usb_rtl28xxu to /etc/modprobe.conf and reboot), or enable some compile-time option (you would need to recompile the odmosdr drivers and probably have root, i wouldn't bother with this and use blacklisting).
you will probably find some better ubuntu-specific advice on the internet