Thread resurrection time.
I'm having the same exact problem with my rikaline unit. I'm not using a usb extension cable, it's directly connected to the computer. It used to work perfectly, but then it started to get wacky.
iGuidance would only update every few minutes or so. It would show that i'm connected to 6-8 sats, but the NMEA info box would show a NMEA line then freeze and update after a few minutes.
Now the past couple of days I'm not even locking on to any sats. I've read some thraeds that this might be related to the internal battery, I'll have to check that.
But has anyone else experienced this problem as well? were you able to resolve it?