I find it strange that Java 6 Update 25 won't work with your machine.. Both Update 7 and Update 25 are basically the same except that Update 25 includes some security updates that are vital to your computer security when surfing the internet.. Going back to Update 7 could cause your computer to become infected should you surf the internet at the wrong sites.

So... first we need to know the operating system you're using, including which service pack it has installed.. For example: Are you using Windows XP SP3? Something else.

What type of credit card "machine" are you using? It must be connecting to the internet but why does it need Java? Have you tried checking the machine manufacturer's website to see if there are any firmware/software updates for the credit card machine? It might be the ideal solution so you can keep Update 25.

Next, what have you tried in order to remove Java 6 Update 25? Normally, it should be easily removable using the Control Panel/Add-Remove Programs section.. If it's not uninstalling correctly, what type of errors are you seeing? We need the EXACT error message please.

There is a Java removal tool (JavaRa) at the link below which might help. Download the .zip file to the computer, unzip it to a folder of choice, then run the Javara.exe.

http://raproducts.org/wordpress/software

Next, in order to reinstall Java 6 Update 7, you'll need to have an installer to do so.. You should be able to retrieve an older version of full offline Java installer by finding it at the site below:

http://www.oldapps.com/java.php

Hope this helps and let us know more.

Grif