Clarion10 tries to open <file>.cwproj.lib while building

Thats a bit serious: Suddenly I get this error when building with MSBUILD or Clarion10

“e:\pr\bayermon\slsc10\app\sl1.cwproj” (Standardziel) (1) ->
(CoreCompile Ziel) ->
e:\pr\bayermon\slsc10\app\map\release\sl1.MAP(1,1): error : File not found or cannot be open: slsdb.cwproj.lib [e:\pr\bayermon\slsc10\app\sl1.cwproj]

With Clarion IDE I get "File not found or cannot be open: slsdb.cwproj.lib.

This dll / app is the root dll of a multi dll project. I dont find any text like this in the cwproj files. When I delete slsdb from the referenced projects node and put it as slsdb.lib in the “library, Objects and Resource Files” all works fine. Until I generate the app again. This is the second time with this problem. Yesterday I have to set up a new solution to rebuild the cwproj files - after that all works fine.