internal error: Network is already in use by interface virbr0

HI! I'm using libvirt 7.7.0 on openSUSE Tumbleweed. Until recently everything just worked. But now my virtual NAT network is not usable anymore. Starting a VM I get this error: # virsh start ae-dir-suse-p1 error: Failed to start domain 'ae-dir-suse-p1' error: Requested operation is not valid: network 'vnet1' is not active Manually starting the network does not work either: # virsh net-start vnet1 error: Failed to start network vnet1 error: internal error: Network is already in use by interface virbr0 In syslog I find: libvirtd: 6325: error : networkCheckRouteCollision:296 : internal error: Network is already in use by interface virbr0 What does that mean? Where to look for a config error? Ciao, Michael.