Volvo: Brake Failure - Stop Saftely

Question
Car: 2004 Volvo XC70
Mileage: 122,000+

2 days ago (Tuesday) I started my car and I got a "Brake Failure - Stop Saftely ASAP."  The next day the car came up with a "Engine System Check."  The car brakes work cause I drove it and it still works.  The car turns on just fine.  The only lights that appear is the "brake" and the "ABS."  I heard that this is a common problem with volvo.  Is it just a ABS control module?  Is it easy to fix it myself?  Can I still drive the car with this problem.  My brother has a 2004 Volvo S80 and he had this problem with his car last year.  The only thing that was wrong with my car before this problem appeared was that I had a "SRS airbag urgent" warning sign on because I disconnected the positive side of the battery when trying to install my aftermarket radio oops.  Can I still drive the car without fixing this issue.  I noticed just today that the brake issue warning light went away and all i have is the engine system check.  I bet it will come back again.  Thank you so much.

Answer
The after market radio can cause srs because the can signal runs in and out of the factory audio .As for the abs ,your probably looking at replacing the control module for thst one .There are some companies that rebuild them ,have a look around the internet ..