This is an issue raised before: Synchronise folders problem but not resolved.
I have a Catalog that will not allow me to synchronize my folders: Library > Synchronize Folder... the option is greyed out & not available via right-click either. (I am trying to sync folders not Collections)
I am using LR5.7 on Win 7 64bit. I tried the LR Repair option in the installer & a cold reboot as suggested in the previous post. None of these cleared the problem.
I have now been through 18 backups of the Catalog, going back 2 months & they all suffer from the same condition. None of my other Catalogs have the problem, which suggests a corruption of this individual Catalog.
As I have many Virtual Copies stored in the Catalog I am concerned these may be lost.
Can anyone suggest a way to fix the issue? It seems to have been mentioned in the forums over the years & no LR technician has ever produced a solution!
As a last resort I will 'Export as Catalog' & see if it corrects the problem.
Workaround: Lightroom Synchronize Folder... Greyed Out
With this workaround, you may clear the issue, retaining the Virtual Copies, but you will lose any Publishing Settings.