PROTEL 99 SE中，进行DRC检查出现如下错误是什么原因：

Processing Rule : Broken-Net Constraint ( (On the board ) )
Violation Net VCC is broken into 4 sub-nets. Routed To 89.29%
Subnet : SW1-2 SW1-5 EC2-1 C6-2
Subnet : R22-2
Subnet : R26-1 U1-1 C9-2 U4-8 R25-1 S5-1 C8-2 U3-8 R20-2 U5-1
C7-2 U2-31 U2-40 C5-2 U6-1 Q4-1 Q5-1 R1-1 Q3-1 Q2-1 Q1-1
LCD1-15 LCD1-2
Subnet : R21-2
Violation Net GND is broken into 3 sub-nets. Routed To 95.65%
Subnet : EC2-2 C6-1 S2-5 S2-6 S2-4 D2-1 Q6-1 S1-11 KEY2-1 S1-5
Q7-1 KEY2-2 KEY3-1 KEY3-2 KEY4-1 KEY4-2 KEY5-1 KEY5-2 C2-1 S1-10 LED10-2
D1-1 U6-3 BUZ1-2 R17-1 C1-1 C9-1 U2-20 R25-2 U1-3 U4-4 S5-4
U3-4 U3-3 U3-2 U3-1 U5-4 C8-1 U3-7 C7-1 C5-1 LCD1-1 R10-1
R11-2
Subnet : C3-1 C4-1
Subnet : S4-2
Rule Violations :2

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