Okay, misunderstanding. I thought this happens in your code but it is actually a line from the import() sub of constant.

                } else {
                    # Catch-all - what did I miss? If you get this err
+or,
                    # please let me know what your constant's name was
+.
                    # Write to <rootbeer@redcat.com>. Thanks!
                    warnings::warn("Constant name '$name' has unknown 
+problems");
                }
[download]

Your example works here. Perhaps some non-printable characters have sneaked in to your text file or there is a clash (other module or within your code) that uses the same constant? What happens if you change DB_ERROR to MY_DB_ERROR? No better ideas ATM, sorry.