Well IOException usually means that the SD card cannot be accessed (IO=Input/Output). This may happen if the device is shaken too much and the SD card loses contact for a moment. But there may be other reasons also.
i've received IoExceptionError, yestarday and in other 3 time before.
Yestarday i've noted that it happen when GPS signal was lost under a bridge.
When i've received this error i wasn'nt be able to manage the application and i've done a soft reset to resolve.
In another time i've lost lost all my log done after the error.