[sync] Error in Encoder.php

[Robert Carnecky]

I try to sync my Sony Clie TH-55 using client software 'Synthesis 
SyncML'. I get an error

PHP Fatal error:  Call to a member function on a non-object in
.../horde/lib/XML/WBXML/Encoder.php on line 145

Any idea what's wrong?

Thanks
Robert