What's the *exact* version of ASE 15.7 you're trying to install? Are you running XP Home or XP Professional?
15.7 is not supported on XP Home.
As of 15.7 ESD #2, support for XP Professional has been dropped. You can install the product but the server binaries (backupserver, dataserver) will fail to start up due to a missing network-related module/dll (said module/dll is only available in newer versions of the Windows OS, eg, 2008, Windows 7).
Without more details about your ASE and XP versions I'm going to guess the dataserver creation failed due to the inability to startup the dataserver binary, which in turn is due to the missing network-related module/dll, ie, you're trying to install/run ASE 15.7 ESD 2+ on an unsupported version of Windows.