Firebird can not connect to any database defined in "aliases.conf" if file or folder name contains # char.
 Example : myalias = C:\#MyFirstFolder\MyDatabase.FDB

- There is no mention in the aliases.conf file's comment section about that (should be like at firebird.conf)
- It is a common practice to change folder or filenames beginning with # or _ signs to place them to first in the list

The Solution would be, if there would be a "# disabling sign" like: @
 and the engine or any other utilities (like gbak, gfix) would recognize this and ignore any # signs in that line beginning with that
 Example: @myAlias = C:\#MyFirstFolder\MyDatabase.FDB

Thanks !