How do I stop Authorize.net payment transaction key from giving error message?

We take payments through Authorize.net and the transaction key continuously gives us an error message. We change it and it works, but we never know when that's going to happen and it should not need to be changed. Authorize.net has been contacted and they say nothing can be done on their end. Any ideas as to way this may be happening?

It's an error 103 message most of the time.  

Kindly try clearing your browser cache, I have gone ahead and cleared you forms cache, notify us if the issue resurfaces again. Sorry for any inconveniences caused.