hm, strc-reg.mkii has
{#1\ifcase\currententrylevel\s!entrya\or\s!entryb\or\s!entryc\else\s!entryd\fi}%
maybe you have a bugged version (core-reg.tex can also contain that code)
anyhow, replace the first \else by \or
Can you report it to ubuntu developers and sent them a patch. I have the
latest version of ubuntu 8.10 installed.
Thanks,
Xan.
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