1999 Volvo S80 Start Prevent Message Try Again

Sometimes I get the "Start Prevent Message Try Again" message on my vehicle. I was told via phone call by the Volvo dealership to use my key to unlock and lock the doors several times and that would probably slove the problem. I have been doing that for several weeks now and I still have the problem. Is there a way to remedy this without going to the dealership? They are so expensive. I took my car to my local, non dealership mechanic, who only works on Volvos, he could not fix it. If I have to go to the dealership, how much would it cost to repair? Also would it harm the car to continue to drive it with the problem? After a couple of tries it always starts. Sorry I can not donate at this time, we are on a fixed income and husband is at dialysis three times a week!