alzy,
Mapped network drives are only visible inside the user session that have defined them.
So if Abyss Web Server is running as a Windows service, it cannot "see" mapped network drives that you have defined inside your user session (after logging inside your account.) This is how Windows/network drives work and Abyss Web Server cannot circumvent that.
Either run Abyss Web Server inside your user session (and you lose the advantages of its Windows service mode) or try accessing the share using its full UNC path as in \\computer\share\dir1\dir2 (the share has to be readable without logins in that case.)
You can also use the hack described in
http://stackoverflow.com/a/4763324 .