I have built up a circuit consisting of a transformer with 6 secondary windings, 6 bridge rectifiers and a filter stage for each. I connected one of the ends of two bridge rectifier outputs to GND grid in order make a symmetrical voltage supply as seen in the screen shot below. It gives the following error message when I hover my mouse on the erroneous sheet entry points.
Sheet Entry DC+ (Output) net: GND
Error: Nets containing multiple similar objects
Error: Nets with possible connection problems

If it is required, contents of the original sheet of the sheet symbol is as below:

Why does this error occur? Can't I reuse a sub-circuit several times? How can I make this design error free?