Why are blocked files appearing? How are the competing tasks performed?

[Vladislav]

On one of the computers where I use FreeFileSync, when I synchronize the Desktop and Documents folders with their copies located in the D:\Backup\ folder, an access error occurs whenever FreeFileSync try to delete unnecessary files or folders. For example:

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OS on it is Windows XP Home SP3.
Permissions for folders in Windows XP are not regulated (with the exception of "Documents and Settings" subfolders). Programs that can block access to D:\Backup\*. * seem to be absent. Deleting the files and folders specified in the FFS error messages by the Total Commander also impossible. However, if I log on to Windows as a user with administrator rights, then these files and folders can be deleted normally.

I have also a copy of the problem synchronization task, differing only in that the backup is not located on a local disk, but in a network folder. This task is executed without errors.

Testing and fixing the file structure of the disk performed, the antivirus disconnected - does not help. Are there ideas, how to determine the source of the problem?

A passing question. If more than one synchronization task is added to the task scheduler, and all of them are executed when the user logs on, do they not conflict with each other? How do they interact with each other to run consistently?