B4R Question invalid directory

now in the right forum, sorry

Hi
to duplicate a project i have
- made a new project
- copy all files to the new folder
- renamed the project main files to the new project name
- in the menue select "Clear Project"
Compiling is ok..
B4R Version is 3.9
Tools/Path are the same as in the old project

but the first log entry (i think) gives me the IDE-massage : error , "invalid directory"

thanks for all hints
Gerd