What I would do is this:
1. Restart the phone to clear up this problem.
2. Do not use that Navigator app. If you need to Navigate, you can do so within Google Maps.
Also, the last few versions of Google Maps are causing lots of problems for people on different phones. If you updated Maps in the market, you could go back to the default Maps app that came with Android 2.1 with the Eris - which still works fine - by going into settings->applications->manage applications, wait for it to refresh, find Google Maps (it may be just Maps) in the list, tap and then tap the button "uninstall updates", if that button is there in the upper right.
[edit] Ok, I just went back to stock Eris. On my phone, there is no Navigator app. There is a Navigation app in the drawer - this is what comes with Google Maps.
I think that you may have installed a third party app. Try looking in the Market, menu, My apps, and see if it is listed there, and, if it is, then uninstall it.