This error has to do with the pin allocations, if you double click a part and unlock its pins, then double click the pin that is causing the error you will be able to see the electrical type. This should be set corectly to suit your component / design. Most of the time its a non error, but it depends on your design.
Another anoying thing that causes it is placing terminating resistors in line with a pin thats set up as an output. The net from the terminating resistor to the input gets flagged as not having a driving source