Thanks for your advice. I now tried everything relating the way how to define the path. absolute (starting with /), relative (with ./) and, as the file is in a subdir of my home directory, with a ~/...../ .
the solution with the ~/ is correctly substituted with my home path, as the error message points to the correct file.
in my opinion, it is strange that the errormessage quotes the path twice, once with ` and then directly after the first quoting with " and closes then the " quote and the the '.
Has anybody already implemented the nport in verliog-a or verilog-ams? could someone post a code snippet for example?