What are i/o errors? A common symptom of i/o error is seeing a message indicating that your computer is experiencing some problems in reading or writing to a storage device - such as a hard drive, USB drive, SD card or external disk. Why do i/o errors occur? These errors tend to originate due to such causes as a broken USB port or cable, broken or rotting connector, inappropriate designation of a drive-letter, obsolete or incompatible drivers, or even physical or firmware damage on the device itself.