It looks like R1Soft manages it's own lvm.static file to process lvm backups. But sometimes it fails and results an error like the following:
Failed to backup LVM/MD configuration
Failed to execute command 'lvm.static pvs -o pv_fmt,pv_uuid,dev_size,pv_name,pv_mda_free,pv_mda_size,pv_all,seg_all,pvseg_all,vg_all,lv_all --nameprefixes --noheadings --units b --nosuffix --unquoted'
An workaround to the problem is to replace/symlink r1soft lvm.static file with the system lvm file.
mv /usr/sbin/r1soft/lib/lvm.static /usr/sbin/r1soft/lib/lvm.static_back
ln -s /sbin/lvm /usr/sbin/r1soft/lib/lvm.static