On some systems, you need to be an owner of the file (write permissions are not enough) to modify its permissions or timestamp. To overwrite file, you do not own, on such systems, you need to turn off Set permissions and Preserve timestamp options or turn on Ignore permission errors.

Note that you cannot disable preserving timestamp for synchronization, unless you turn off Modification timestamp comparison criteria.

When using scripting, add -nopreservetime and -nopermissions switches to put command.

When using .NET assembly, set TransferOptions as follows:

TransferOptions transferOptions = new TransferOptions();
...
transferOptions.FilePermissions = null; // This is default
transferOptions.PreserveTimestamp = false;