1) - there is no need to perform detach/attach to make a backup !!
That way you'll waste backupspace and you'll have downtime.
- Make sqlserver backups using "BACKUP DATABASE ..." (check BOL) and
have your systembackup scipping the sqlserver db-data and db-log-files.
2) what's the error message ?
3) Did you collect the file-locations and names (sysfiles) before you did the detach ? (maybe someone added a file or filegroup,...)