Cannot access Memory

For some time i cant download my Programm code directly to Flash.
Everytime if i try to download the Code, or erase the Chip, the error Meassage appears "Cannot acces memory" & Error: Flash Download failed - Target DLL has been cancelled.
If i Start the uC in Boot Mode Im able to download the Code, or erase the Chip.
After i downloaded the programm Code i cant access the Memory (except in Boot Mode)
If i read the option Bytes with the Flash loader demonstrator 2.0.0.0 the Read out protection and the Write out Protecion id disabled.

Thanks in advance for any help,
Manuel