ATC keep asking the impossible

Trying to do a simple IFR flight in a Cessna 172, ATC keeps asking me to climb to 18,000 feet.

The poor little thing can't do it. I van ask for a lower altitude, which seems to be granted, but I'm still told to expedite my climb to FL180 Not possible, as far as I can make out.

Am I doing something wrong, or is it a bug?

There is probably an elevation error at one of your flight plan airports. I have had this happen in Sardinia.

Hopefully one of the response choices would be "Unable." :pilot:

 

But since you're on a flight plan, what altitude did you file for?

Unfortunately there is no "unable" option. When this happened to me in Sardinia, I filed the flight plan requesting reasonable altitudes, but it sent me way above ceiling each time. I changed departure airports, filed the plan, and it worked as it should. I could only surmise that there was an elevation error at the departure airport (one of the other forums mentioned that that resulted in the ATC errors).