Unfortunately, this version still not running with PHP 5.3. As I use a patched version and a personalized theme, I do the upgrade by applying a diff between 2.1.5 and 2.1.6 (not provided by the project). No issue with my changes, all seems to work correctly.

Howto (with the version 2.1.5 and 2.1.6 archives download) :

tar xzf dotclear-2.1.5.tar.gz
mv dotclear dc215
tar xzf dotclear-2.1.6.tar.gz
mv dotclear dc216
diff -ruN dc215 dc216 >dc215216.patch
cd blog  # the installation folder
patch -p1 <../dc215216.patch

That's all folks ! :)

For whose who want to path their dotclear to work with PHP 5.3 :

Now, we have to wait to version 2.2 which should be PHP 5.3 compatible.

As I often says, good applications are working with PHP 5.3, so Dotclear seems not one of this category ?