I read this answer here by John Erick:
Navigate to your backup disk using Finder. Manually delete the oldest backup folders (i.e. perform the task Time Machine typically is able to do automatically) then, tell Time Machine to "Back Up Now". You'll be back on track and good to go until the next time you pull in a large amount of data to your source disk while Time Machine is running on a "full" backup disk.
And this is my problem... Will this last solution work on a Time Capsule?
I have a 1TB hard drive IMac with 165GB available space
Problem is after I was doing a lot of reorganising on my hard drive my 1TB Time Capsule/Time Machine suddenly refused to back up with the following message:
THIS BACK UP IS TOO LARGE FOR THE BACK UP DISK. THE BACK UP REQUIRES 855.13GB BUT ONLY 156.73 ARE AVAILABLE. LAST SUCCESSFUL BACKUP WAS 25/6/12 @ 1700.
It also seems to have deleted all previous back ups apart from the successful one at 1700.
How do I get it to start working with incremental back ups again please? Bad timing as I was just about to go and purchase another external hard drive and off load some files from iMAc, now it has caught me out!