"Sensor Error Radar 0:FC." Anyone know what that means?

Getting the same problem. Did a 40 miler yesterday and this popped up probably every 5 minutes!

Report it to Garmin Customer Service for repair/replacement. 
I have sent mine and awaiting for replacement. 
I need to wait 10 days for that, and it should have been replaced on the spot, since the product had a defect as DOA. 

I have recently had a unit replaced due to a sticky power button, the new replacement is showing this error code way too often for my liking..  it took them. 3 weeks to replace the other unit so I wouldn't be impressed if I had to wait that long. again..   

It's better to have it replaced by the shop where you bought it, as they are bound by the consuler law. The service doesn't seem to care about that, nor they can't give you money back if they don't have a product for replacement. I waited more than 10 days, until I had to call them myself and find out what's happening with my RMA. FInally they sent me a new item, which now works good, with no error code. 

Garmin will not replace a unit with this error, they told me there will be an update at some point. No guess as to when,. I told them i wanted my unit replaced because it was onlu 3 months old. They said there was no chance at a replacement. If your unit is new, send it back. I'm moving on from garmin. Absolutely ridiculous to spend this much money and get customer service that says "zero chance".

They told me about an update too, but then I think they noticed that an update won't help, so the device needed to be replaced. 
You could have it returned to the seller, not under Garmin's warranty but under, stating that they sold you a product does not comply with the sales agreement. 
And yes you are right, Garmin's service is very poor. Next time I will not send them anything back, but I will do it via a seller/shop. 

It looks like they didn't fix it in two years. This is crazy.

Got my Varia about a month ago and really thinking to get rid of it because of this issue.

Today I got 10 (!) errors on a two-hour ride.

And every time I need to get my hand off the handlebar to close error message.

Annoying af

Hello, i had this error, first time i used, and then never more!!

My RTL515 did this right out of the box when I bought it earlier this year. It would happen about once every other ride or so. Last couple of months, it suddenly is happening dozens of times per ride. It has become a huge safety issue since the message distracts my attention from the road, not to mention the loss of the radar benefit which is the whole point of having the varia. I'm incredibly frustrated with this. It would not be so bad if it would just beep and turn the radar icon red for a few seconds till it reconnects. But, the message pops up and blocks my workout telemetry, forcing me to touch the screen to clear it. Last ride I got so frustrated I turned the Radar unit off completely. Garmin better fix this soon or this will be the last garmin product I ever buy.