can make in debug, but not in release

using NSight EE 10.2 with Java 8. Writing a CUDA library. I can build in debug, but in release I get the error

make clean
make: *** No rule to make target ‘clean’. Stop.


Errors occurred during the build.
Errors running builder ‘CDT Builder’ on project ‘CUDAwithM-v2’.
org.eclipse.cdt.managedbuilder.internal.core.ResourceConfiguration cannot be cast to org.eclipse.cdt.managedbuilder.core.IToolChain

I did a websearch, and seems to point to a problem in the naming of the make file.

a) how can I fix this?
b) why does this not show up in debug? What’s different?