we always meet this phynomenon "this pin is already assigned when we pin the pins"

问题描述:

we always meet this phynomenon "this pin is already assigned when we pin the pins"
however ,when we found a new project this error lost.
i want to know why this happend to me sometimes.
if you knew ,please tell me

in the project there are many pins your defined,and you need to assign a pin number(pin of the CPLD or FPGA) to the pin you had defined.But you should not assign the same pin number to the different pin which you defined yourself.