To reproduce the issue follow the steps:
1. Create new project
2. Download dll's user has attached ( ENet.dll, ENetCS.dll)
3. Try imporint dlls in the project
4. Create and attach simple script to test functionality of the library
try {
new ENet.Host().Create(null, 1);
} catch {
Debug.Log ("Error");
}
5. Run the project, console error is displayed
6. Create standalone project
7. Add DLL file to the folder where executable is built
8. Run standalone project
9. Console error is not displayed in "output_log.txt"

Reproduced in 5.3.5f1, 5.4.0f3, 5.5.0a5