Objective Development Forums

Hello,
Im relatively new to USB, but tried to develop a very small application, where I can connect with a Terminal (Hyperterm or similar) and press one button to lighten up an LED and press another button, to let it switch off again.
This is meant to get some experience with the CDC Things for a later project.

My Problem now is as follows: The device enumerates flawlessly, but when it comes to sending or receiving data through the bulk endpoints (in the CDC Data class), i often get stalls.

I uploaded my sourcecode, usbconfig and a USB Log (Be patient, 2,5MB HTML File) here:
http://wayne.klinkerstein.m-faq.de/AVRUSB/Main.c
http://wayne.klinkerstein.m-faq.de/AVRUSB/usbconfig.h
http://wayne.klinkerstein.m-faq.de/AVRUSB/UTLog.html

Have a look at packet #106 and #360 (and subsequents).
I hope you can give me a hint where my problem could be.
Thanks in Advance.