This means that an interrupt happened that no driver expected. It's unlikely that the hardware issued an interrupt by mistake. It's more likely that the software has a minor bug and doesn't realize that some software did something to cause the interrupt. In many cases you can safely ignore this error message, especially if it only happens once or twice at boot-time. For boot-time messages, look at the messages which are nearby for a clue as to what is going on. For example, if probing is going on, perhaps a probe for a physical device caused that device to issue an interrupt that the driver didn't expect. Perhaps the driver wasn't listening for the correct IRQ number.