Avic N1 navi issues

[dhouse]

I have and Avic N1 and a Avic D2. I am not having any issues with the D2. I do share the disks between the two of them. My wife has the N1. A while back, I gave her the disk (70MT) to run an errand and the navi screen froze up. She took the disk out and did it again and it gave the message "preparing to switch to memory navi mode" and below that it says it may take 30 seconds and not to remove the disc. The problem is that it freezes there I have to hold hte eject button down for a while to get it to actually eject the disc. The rest of the unit works fine such the DVD videos, radio, rear view cameras, rear seat monitors etc. I am only having issues with the navi. I just put the disc in and rebooted and nothing changed. I then put the disc and shut of the power a few times and then I got it to bypass the message and got into navi settings. Everything works well in settings except when it has to read the map or anything audible. It does eventually read and speaks but it is extremely slow. It acts as if there is not enough memory to read the disk fast enough. Does anyone have any ideas on this one? Is there a way to clean the memory other than the reboot button on the front of the unit? Please help as soon as possible as I have to leave for vacation in 7 days. Thanks in advance.