stk500_getsync() not in sync: resp=0x7d

Hello, I have an Arduino from the Franzis Starter Pack and scince several days I can not upload any program to the device. The only output from the console is the following:

stk500_getsync() attempt 10 of 10: not in sync: resp=0x7d

This will be shown 10 time (for 10 tries).

Does anybody have any idea what this error means?

Assitionally the connection is correct, because everything worked before.

May I destroyed the bootloader?

pls help