Referenced file 'file' is not an assembly; use '/addmodule' option instead
An output file (output file 1), produced in a compilation that used /target:module (does not have an assembly manifest), was specified to /reference. So, rather than appending an assembly to the assembly for the current program, the metadata information in output file 1 will be added to the assembly for the current program.
Output file 1 must be in the same directory as (or in a subdirectory of) the assembly manifest file for the current compilation.