SyncToy 2.1 and file access problems

I have SyncToy 2.1 installed on a laptop. I have set up pairs to sync folders from my PC to the laptop. All fine apart from some photo folders. I have around 16k photographs in about 60 folders. These all sync apart from about 1.5k photographs in 5 or 6 folders. I get "Cannot read from the source file" and "Access is denied" Exception from HRESULT: 0X80070005 E_ACCESSDENIED errors.

I have put on and taken off sharing on the root photograph folder but still get same errors. Any ideas?

Goggling does throw up a few ideas but no real solutions.