Weird Dreamcast Disk Drive Error

I just got a neat Dreamcast with controllers, cables and games for $20 USD at a Thrift Store. It powers up great, but I run into problems when I put in a game the disc spins up and says "Please wait while disc is being checked", this flashes on a off randomly and then stops and when I click the play game it says "Please insert game Disc".

Here is the weird thing, if I let it sit for about 20 seconds, the disc spins up, loads and the game starts for about 10-20 seconds, then it stops spinning and it goes back to main menu with the Please insert game Disc error.

Is there a way to fix this error because the drive seem to work (because the game starts up for short periods of time).

Thanks for your help!!