Help in marking a partition 'not active' for system backup

I set my Win 7 64-bit Pro to backup my files and do a system image once a week on a 1TB SATA disk. As of last week, I had only used 450 GB of that disk for the backup process that included a couple of system images of my C: drive (I let Windows decide on how many images to keep).

Today, I get an error message that the backup had failed because the backup disk did not have enough space. I looked at the disk and there was 550GB of space still available, so I was confused.

I looked at the parameters of the system backup and found that this time the backup would make a system image of my C: drive and my E: drive (the 2TB drive that keeps all my games). This was not there for the last backup run.

I looked at the parameters for the E: drive and found that its partition was marked 'active' (the only other active partition was my C: drive and I have two other drives installed too but not 'active').

How do I mark the E: drive partition 'not' active so it gets removed from being imaged?

I successfully marked the E: drive partition as inactive per your instructions, check the status of the drive in Disk Management, and re-booted the PC. Thanks.

However, when I enter 'change settings' in system backup and select the 'Let me choose' parameter, the 'include a system image of drives C: and E:' still appears (even after a re-boot). If I select 'Let Windows choose' I don't know if it'll choose both drives now or just the C: drive.

Is there another way to have Backup make a system image of only the C: drive?

Thanks again for your help!

Nothing's been moved except some savegames from my Documents/My Games folder to a folder on the E: drive.

Now it seems the same problem is happening on my wife's Win 7 Home Prem PC. I checked her backup parms and found that a data storage only drive had been added to her backup in the same menu choice as 'Let me decide....'. Backup was doing a system image of that drive along with her C: drive. However, when I unchecked her storage drive and rebooted, backup still thought it would do a system image of that drive.

Is there anywhere I can go in the registry to correct this?

I've attached two screen captures. One shows the backup parameter with C: and E: and the other is the disk management screen.

Let me know what you think.

Thanks for all the advice. I'll try these and get back to you this afternoon.