This problem may be due to a change in the way the fitter checks pin spacing rules for unconnected design output pins from the Quartus II software version 4.2.
In the Quartus II software version 4.1 and earlier the fitter treats all unconnected design output pins as non-toggling outputs. This allows output pins that are unconnected in the design to bypass the pin spacing rules for the target device. These pins may, for example, be placed next to differential pins which have specific pin placement rules. Consult your device datasheet or handbook for information about pin placement rules.
The pin-spacing checks are tighter in the Quartus II software version 4.2 than in previous versions. The fitter assumes that all types of pins, including output pins that are not connected to anything in the design, are toggling pins and therefore enforces all pin-spacing rules.
In the case that your output pin is intentionally stuck at GND or VCC (i.e. it does not toggle), assign the pin a 0 MHz toggle rate using the Assignment Editor. The fitter then treats the pin as a non-toggling pin during pin-spacing checks.
Remember that it is important to change the 0 MHz toggle rate assignment if you decide to change the output pin to an active toggling pin, to avoid violating pin-spacing rules.