The Memory Bank/Byte Planner does not allow signal groups to be assigned to I/O banks that are already assigned to non-memory I/O ports. A yellow warning icon appears with a tooltip indicating that non-memory ports are assigned to the byte group, as shown in the following figure.
Figure 1. Warnings for Assigned Non-Memory Ports
You can address this issue by unplacing the ports. In the I/O Ports window, right-click the ports, and select Unplace, as shown in the following figure.
Figure 2. Unplacing Non-Memory Ports