Time Machine Could Not Complete The Backup

Hi

My HDD on my previous iMac died and I took the opportunity to upgrade to a new 27" iMac. It is a Solid State drive to host all the applications and a 2tb drive to hold all my files (mostly images).

I restored my previous set up from the Time Capsule and everything went well, and spent a day upgrading and tidying all my application files. At the end of that day I re-set the backup on the time machine to just back up the solid state drive i.e. the apps and the core operating system so that in the event of another failure it could be used to restore from.

Everything was working well for a few weeks,but recently the back up has been failing. I get the following error message:

"The backup disk image “/Volumes/Time Capsule-2/Andy’s iMac.sparsebundle” could not be accessed (error -1)."

Looking at the support/help seems to suggest this is because the disk inst available, yet the blue time capsule shows as an icon on my desktop, as does the green time machine backups icon when it is trying to back up. The last backup is now about two weeks old and I have recently added a few new apps so am keen to resolve this issue. I have tried re-directing the back-up to the time capsule disk,but it still fails.

This afternoon I tried to force a backup rather than wait for a scheduled time, and got another essage similar to the one above that suggested the disk was in use by another

Does anyone have any suggestions as to how to best resolve this issue and to get the backups working again?

Any ideas greatly appreciated!

Many thanks

Andy