problems reading codes on a 97 Z24

The other day my cel came on so I hooked up my scanner. ussually it will then say "read" then I turn on the key then in about 10 sec or so it will pop up with the code(s). well this time I plugged it in and nothing happened, so I pressed the "link" button and it said "error". I've read the codes on this car before no prob so I thought the scanner was having problems, so I hooked it up to a few other vehicles and it read them fine. So the next thing I did was unhook the batt. on the car for about 15 minutes, I knew I would lose the code but I thought that resetting the computer would let it link up with the reader. Well I thought wrong, the cel hasn't came back but it still won't link up. Any ideas why all of a sudden it won't link? How can I get it to link? Thanks in advance for any info.