backup domain file

I took a backup of a domain using this command:

%asadmin> backup-domain --domaindir /var/opt/SUNWappserver/domains --verbose=true domain1

successfully found a sjsas*V0001.zip file in installdir/domains/domain2/backup folder.

When I tried to open it to check for the files in from local system and see an error:

Cannot open file; it doesnot appear to be a valid archive..

Can anybody tell me what this error mean?

When I viewed the error output from WinZip, this is what I get:

End-of-central-directory signature not found. Either this file is not a Zip file, or it constitutes one disk of a multi-part Zip file.

[663 byte] By [G_identitya] at [2007-11-27 4:43:21]
# 1
I am using SUN Java System Application Server8.1EE.
G_identitya at 2007-7-12 9:55:06 > top of Java-index,Application & Integration Servers,Application Servers...
# 2

asadmin> backup-domain --domaindir /var/opt/SUNWappserver/domains --verbose=true domain1

May 17, 2007 4:13:20 PM com.sun.enterprise.config.backup.LoggerHelper finest

FINEST: Request DUMP **********

Class ModifiersFieldValue

BackupRequest static final excludeDirs [Ljava.lang.String;@15093f1

BackupRequest (package)domainsDir/var/opt/SUNWappserver/domains

BackupRequest (package)domainNamedomain1

BackupRequest (package)description 1179432800024

BackupRequest (package)backupFile/var/opt/SUNWappserver/domains/domain1/backups/sjsas_backup_v00001.zip

BackupRequest (package)domainDir/var/opt/SUNWappserver/domains/domain1

BackupRequest (package)timestamp1179432800024

BackupRequest (package)backupDir<null>

BackupRequest (package)tersefalse

BackupRequest (package)verbosetrue

May 17, 2007 4:13:20 PM com.sun.enterprise.config.backup.LoggerHelper fine

FINE: Writing /var/opt/SUNWappserver/domains/domain1/backups/sjsas_backup_v00001.zip

com.sun.enterprise.config.backup.BackupException: Error writing Zip file: /var/opt/SUNWappserver/domains/domain1/backups/sjsas_backup_v00001.zip

G_identitya at 2007-7-12 9:55:06 > top of Java-index,Application & Integration Servers,Application Servers...