I found the error, btw. the bug.
If i create a Design and save it with Uppercase-Letters, then this error raised.
It looks like, the compiler / android search for the .bal in lowercase letters, but if the app has stored .bal's with uppercase letters, the release compiling goes wrong.
This explains the error-message.
After Renaming the .bal's to lowercase, the released compilated app works fine.
JimJim
XUN