The exact error message was (re-translated to english):
Preparing to replace libc6 2.4-1ubuntu10 (with .../libc6_2.4-1ubuntu12_i386.deb) ... Matching libraries: /usr/lib/libpthread.so.20 /lib/ld-linux.so.2
A copy of glibc was found in an unexpected directory. It is not safe to upgrade the C library in this situation; please remove that copy of the library and try again.
The exact error message was (re-translated to english):
Preparing to replace libc6 2.4-1ubuntu10 (with .../libc6_ 2.4-1ubuntu12_ i386.deb) ... libpthread. so.20 /lib/ld-linux.so.2
Matching libraries: /usr/lib/
A copy of glibc was found in an unexpected directory.
It is not safe to upgrade the C library in this situation;
please remove that copy of the library and try again.