home wireless network

I recently got a new macbook pro and I'm having trouble using my printer on my home wireless network. Every once in a while it will work fine, but usually, the printer shows an error message that " IP address that was just configured is already at use on the network. " I am guessing that it's meaning an IP address that is assigned by my wireless router. I wonder if anyone can tell me how to solve this problem. Thanks.

Help us out with more info -
The printer is showing this error on the front panel?
What method/protocol did you use to set up the printer on the Mac? Bonjour or IP?
Some routers and devices re-use a same IP address if your Mac is turned off. To check what is going on, we need to know what the printer's IP is and what your computer's IP is. (and who knows, maybe a neighbor was using your internet, too)

Thank you for the response. Yes, the Epson Workforce 600 shows the error message on its little screen. Actually, I never set the printer up on the Mac. I thought it was just using bluetooth. I sort of figured someone else may be using my router, even tho it is password protected. It does work every once in a while. Address of the printer is 192.168.1.2. Address of the Mac is 192.168.1.6.

You were probably using Bonjour - which is what the printing system defaults to, and what the driver prefers. Bonjour is Apple's automatic network browse and print software.

Since the IP addresses aren't the same, I'm going back to my guess that someone else was using you're internet. You do have it password protected, right (WPA or WPA2)?