Backup error - not part of a multiple family media set

I am new to SQL 2005. I have setup and new maintanaince plan of making backup on to different paths but i encountered an error saying

Executing the query "BACKUP DATABASE [promis_05] TO DISK = N'E:\\ERP Database\\ERP Backup\\Promis_05', DISK = N'\\\\backupsrv\\ERP Backup\\Promis_05' WITH NOFORMAT, INIT, NAME = N'promis_05_backup_20061111181236', SKIP, REWIND, NOUNLOAD, STATS = 10
" failed with the following error: "The volume on device 'E:\\ERP Database\\ERP Backup\\Promis_05' is not part of a multiple family media set. BACKUP WITH FORMAT can be used to form a new media set.
BACKUP DATABASE is terminating abnormally.". Possible failure reasons: Problems with the query, "ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.

We did not know what to make of this.

1) Is it bcoz i am backing up the database on 2 locations same time.

2) What is BACKUP WITH FORMAT?

3) Why won't it let me add a new file that is not part of the 'family' ?

4) How does it get to be part of the family?

Thought and ideas are highly appreciated!

When you back up to two files, you are creating a stripe set. The restriction is that all backups sent to a media set must have the same number of stripes. That's the meaning of your error.

You need to create a media set with the number of stripes you want to use. You can't add members later.

The method for creating a new media set is to use the WITH FORMAT option on your backup command. This is the equivalent of reformatting a tape for backups. It wipes out any previous data in the file(s), and sets up the headers correctly.

So, if you issue the same command in your script, adding WITH FORMAT for ONE TIME ONLY, the first time you use that media family, you should be good to go. From then on, you can just use it as your script is now.