Error: Can't place multiple pins assigned to pin location

Description

You may observe this error message if you have a signal in your design that has been assigned to a Dual-Purpose pin, but you have not changed the appropriate Dual Purpose Pins setting in the Quartus® II software to enable this.

Resolution

To solve this, go to  Assignments -> Device... -> Device and Pin Options... -> Dual-Purpose Pins, and change the value of the appropriate pin to Use as regular I/O.