为什么我一直提示这个错误

[UnoDean]

Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <GTMRefresh.DefaultGTMLoadMoreFooter 0x7f9fe1e4e3b0> for the key path "contentOffset" from <UICollectionView 0x7f9fe3287a00> because it is not registered as an observer.'

[GTMYang]

@UnoDean iOS版本多少？