For performance reasons, the module system now
hopes that Modules/*.xml files are in a rigid file
format - the exact format that it in fact writes
them out in. If it finds them in this exact
format, it can parse them more quickly than with
an XML parser.

AU, however, writes out files in a slightly
different way. This causes the module system to
have to fall back to the full XML parse, wasting a
bit of startup time. For example, install treefs
from AU and restart and you will see:

[org.netbeans.core.modules] Note - failed to parse
Modules/org-netbeans-modules-treefs.xml the quick
way, falling back on XMLReader

Please look at
org.netbeans.core.modules.ModuleList and copy that
exact formatting, byte for byte. If successful,
AU-generated XML files should exactly match the
module-system-written ones, and this warning will
not appear.