I too am having this problem and have emailed btcloud.support@bt.com with my account number
waiting to see if any thing happens.
Mark S
After several calls with the BT Team I was eventually told that they have a problem with the system and were working on a fix to the version history issue.
Until they had sorted this out I was told that if the storage limit was reached then it would be increased to allow the bac up to continue.
Well today the limit was reached and the system is showing that "Sync Pending There is not enough space"
I have filed another complaint, so we will see what happens now.
