I ran into an incompatibility with TWiki 4.2.0 (and above) and Perl 5.8.4. This is Perl bug 22238.

The error is:

Bizarre copy of HASH in leavesub at $TWIKIDIR/lib/TWiki/Plugins/TablePlugin/Core.pm line 73.
[...]

And the fix:

cd $TWIKIDIR
sed -i \
    -e 's/my %defaultCssAttrs = ();/my %defaultCssAttrs;/' \
    -e 's/%cssAttrs = ();/%cssAttrs;/' \
    lib/TWiki/Plugins/TablePlugin/Core.pm