When using BTSync to synchronize volume E:\ I happened to encounter a strange behaviour: After a while new files were not synched although BTSync claimed to have done so. After heavy testing I noticed an even more strange behaviour: Folders alphabetically preceeding the folder 'System Volume Information' were not mentioned when synching neither single files in the root folder. Trying to re-index folder E:\ (remove then re-add the folder) would suddenly lead to consider only a few files instead of thousands being on the volume. Enabling debug logging uncovered the following error: Got error 5 while obtaining file info for \\?\E:\System Volume Information. After encountering this error, BTSync stopped synching (but claimed that synching was sucessfull). The folder 'System Volume Information' was at first not accessible to view its content, I had to add appropriate rights (added it to the group of Administrators). In there I found a file named 'tracking.log'. After the date of the timestamp of that file, BTSync had stopped working properly. When I had given access to 'System Volume Information' folder, BTSync worked properly again. The file 'tracking.log' is created by 'LocalSystemNetworkRestricted' via svchost.exe (One can verify this by using e.g. the Windows 7 resource monitor). It seems to be created in the root folder 'System Volume Information' on every drive. So what exactly happened? BTSync tries to scan every folder (starting alphabetically at the last one), encounters missing access rights on 'System Volume Information'. It then stops working but claims that synchronizing has been done. Solution: Grant access to the folder and BTSync will work properly again. (It does not help to simply exlude that folder in the .SyncIgnore file) Maybe this my observation may help someone.