An input/output error occurred. This may signal incorrect handshaking protocol or improperly terminated or faulty cables.

I once got rid of an ioerror by cleaning up the hard disk of my RIP. Maybe this was a coincidence but it may also show that ioerrors can point to a lack of resources (RAM, swap space,…) on the PostScript RIP.

Virus scanners can be another source of ioerrors because they try to intercept the creation of a file and cause a conflict with Distiller or RIP software. On a forum I read about a user who got rid of ioerrors by (temporarily) deactivating Norton Anti-virus.

Offending command: random characters

If the offending command is just a series of random character, this may indicate a problem with the communication link; check your network, communication settings, disable spoolers or run the job again. You could also reinstall the printer driver because it may be corrupted.

Other errors

There are several commands that can cause “IO error” PostScript errors. Check the specific offending command to get a more detailed error description: colorimage, image, readstring