Fatal error: Call to undefined function iconv_set_encoding() in /home/www/motorrad/html/wp-content/plugins/umapper/Zend/XmlRpc/Client.php on line 216
This message you'll get if php is compiled without iconv support I think.
So I removed (commented) the iconv_set_encoding calls, because my page is already running in utf-8, should be no problem.
But then the next Problem:
Fatal error: Class 'DOMDocument' not found in /home/www/motorrad/html/wp-content/plugins/umapper/Zend/XmlRpc/Request.php on line 357
I think my reduced PHP (5.3.5) compile doesnt bring all needed classes (php-xml I think). :-(
So if you want to use UMapper, be sure that iconv and libxml is compiled into your php installation.