Proteus 6 errors when trying to assign VDD pin

The Power-Up Timer is also enabled through the configuration bits. The Power-Up
Timer or PWRT provides a time-out period to allow the VDD to rise to an acceptable
level to prevent ambiguous operation.
It operates on an internal RC oscillator that provides a nominal 72ms delay.
When Brown-Out Reset is used the Power-Up Timer is always enabled. Power-Up
Timer is always enabled when Brown-Out Reset is enabled, even if Power-Up
Timer is disabled. They work together to allow VDD to rise to an acceptable level
after a Brown-Out Reset .
Please see your device specifications for Power-Up Timer .

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Brown-Out Reset
BOR resets the CPU
* Triggered when VDD to drop below VBOR
* BOR will continue to reset part if voltage is below VBOR
* When VDD rises above VBOR, the device is held in reset for additional time by PWRT
* BOR is re-triggered if VDD drops below VBOR

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use proteus 6 for simulation

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