Run 'which astdb2sqlite3' from a terminal. If no filenames are displayed, then astd2sqlite3 has not be installed. Check if the distro includes it in another asterisk related package, or download the Asterisk 10 source from the Asterisk.org website and follow the normal build instructions. Instead of running 'make install', manually run 'utils/astdb2sqlite3 /var/lib/asterisk/astdb' from the Asterisk source directory, replacing '/var/lib/asterisk' with the 'astdbdir' directory listed in asterisk.conf. After the conversion, the distro-supplied Asterisk should successfully run.
Migrating back from Asterisk 1.8 to Asterisk 10
If migrating back to Asterisk 1.8 from Asterisk 10, it is possible to convert the SQLite 3 internal database back to the Berkeley DB format that Asterisk 1.8 uses by using the astdb2bdb utility found in the utils/ directory of the Asterisk 10 source. To build, make sure that astdb2bdb is selected in the Utilities section when running 'make menuselect'. Running 'utils/astdb2bdb /var/lib/asterisk/astdb.sqlite3' (replacing '/var/lib/asterisk' with the 'astdbdir' directory listed in asterisk.conf) will produce a file named 'astdb' in the current directory. Back up any existing astdb file in the astdbdir directory and replace it with the newly created astdb file.