For whatever reason, a customer wanted to have his database in a directory which contained a Hash character (#) in its name.

So the entry in aliases.conf looked like this

mydb = D:\#kit\subdir\mydatabase.fdb

The hash sign, however, starts a comment in aliases.conf. We could only work around that by selecting another directory (which can be
difficult when you have fixed naming conventions on a customer server).

Quoting the database filename doesn't help in Firebird 1.5.5. It just changes the error message when you try to create that database.

I also did a test with Firebird 2.1 with a quoted filename:

mydb = "D:\#kit\subdir\mydatabase.fdb"

With the above alias string, when I do a CREATE DATABASE, a file named MYDB (the name of the alias, without any extension) is created in the Firebird\bin (!) directory.

So there seems to be a problem with hash signs in alias filenames. I know this seems to be a rare case, but you can never know what crazy path naming conventions you find on customer's systems ...