Hi, bug #448249 has broken all reverse dependencies of apt in squeeze-security because they need libapt-pkg-libc6.7-6-4.6, but apt 0.7.20.2+squeeze1 provides libapt-pkg-libc6.9-6-4.6 instead. :-/ This needs to be fixed ASAP, there are already complaints on debian-user about aptitude, synaptic and other programs removed during dist-upgrades in testing. Sven