I realized we have not been "closing" the CDs we've been sending out to customers. I've heard and experienced issues with this many years ago. I'm wondering if this only happens on older computers or some newer ones will have this issue. I'm thinking this issue is not on any drives newer than 5 or 6 years old. It was at least 10 years ago that I ran into it.
Also, I remember when this happened that the drive just couldn't read anything on the CD and acted like it was full, but just couldn't read any of it. Does anyone know if this is the typical behavior? Or what else will happen if this error shows up?
I assume you are referring to closing a session when writing CDs. If you don't close a session properly, you risk the CD not being readable in other players. This is true of both CD writing software and using DLA to use the CD in a similar manner to a floppy. According to the Wikipedia DLA article, this can also lead to crashes and lock-ups in some windows varients.
If your CD is not closed, doesn't that mean more data can be added to it in the future? Things like viruses and malware? I do know that the Table of Contents is not written to the CD or DVD until it is closed, meaning that most players can not play it because that is the first thing they look for.