Ok. i found the Files. All who have the same problems like me when using Strings:
Follow these instructions:
http://code.google.com/p/arduino/issues/detail?id=857
and download the malloc.c file here:
http://code.google.com/p/arduino/issues/detail?id=468
You have to put them here: arduino-1.0.1/hardware/arduino/cores/arduino
A special Thanks to these guys who have written the code as far as I understand;
Joerg Wunsch
Gerben van den Broeke
Paul Stoffregen