关于层次电路图ERC的问题

各位高手:
我在做三级层次图时,ERC检测时发现问题如下:

#1 Error Duplicate Sheet Numbers 0 main.Sch And POWER
#2 Error Duplicate Sheet Numbers 0 main.Sch And OSC
#3 Error Duplicate Sheet Numbers 0 main.Sch And ADC
#4 Error Duplicate Sheet Numbers 0 main.Sch And A-D-1
#5 Error Duplicate Sheet Numbers 0 main.Sch And A-D-2
#6 Error Duplicate Sheet Numbers 0 main.Sch And A-D-3
#7 Error Duplicate Sheet Numbers 0 main.Sch And A-D-4
#8 Error Duplicate Sheet Numbers 0 POWER And OSC
#9 Error Duplicate Sheet Numbers 0 POWER And ADC
#10 Error Duplicate Sheet Numbers 0 POWER And A-D-1
#11 Error Duplicate Sheet Numbers 0 POWER And A-D-2
#12 Error Duplicate Sheet Numbers 0 POWER And A-D-3
#13 Error Duplicate Sheet Numbers 0 POWER And A-D-4
#14 Error Duplicate Sheet Numbers 0 OSC And ADC
#15 Error Duplicate Sheet Numbers 0 OSC And A-D-1
#16 Error Duplicate Sheet Numbers 0 OSC And A-D-2
#17 Error Duplicate Sheet Numbers 0 OSC And A-D-3
#18 Error Duplicate Sheet Numbers 0 OSC And A-D-4
#19 Error Duplicate Sheet Numbers 0 ADC And A-D-1
#20 Error Duplicate Sheet Numbers 0 ADC And A-D-2
#21 Error Duplicate Sheet Numbers 0 ADC And A-D-3
#22 Error Duplicate Sheet Numbers 0 ADC And A-D-4
#23 Error Duplicate Sheet Numbers 0 A-D-1 And A-D-2
#24 Error Duplicate Sheet Numbers 0 A-D-1 And A-D-3
#25 Error Duplicate Sheet Numbers 0 A-D-1 And A-D-4
#26 Error Duplicate Sheet Numbers 0 A-D-2 And A-D-3
#27 Error Duplicate Sheet Numbers 0 A-D-2 And A-D-4
#28 Error Duplicate Sheet Numbers 0 A-D-3 And A-D-4
请问是什么原因导致的?谢谢 !