Don't auto clean your drives. Set CommVault to auto-detect when the tapes need cleaning--either by error count or by hours of use.
For Simpana v10, here's how you get to that setting:
Click Home, then Control Panel, then under Storage click on Hardware Maintenance.
From there, click on the Drive Cleaning tab. Highlight your drive type (not your tape type) and click Edit.
In my experience, Simpana's default values were kinda high when I was on v9. To get to this setting, go to Home then Control Panel, then Storage/Hardware Maintenance.
I've attached a screen shot of my settings. Note that the setting you need may vary dramatically, based on things like quality of tape media, temperature, and humidity.
Aside from that, if you set the library to auto clean, you may need to reserve a slot for that to work and that tape may then be hidden from Simpana, so if you want to use Simpana to detect cleaning needed and/or clean based on hours, I think you'll need a second cleaning tape in the library, but located in a non-cleaning slot.
Library auto cleaning has never worked well for me, it always winds up cleaning way too late and I presume that's why you're setting it to clean at a scheduled time. When it is past time to clean the drive, I've found that both aux copies and restores gradually slow to a crawl but don't start failing until it gets really really bad. Your mileage may vary.