my xk8 won't start
 

I have been having problems with starting my '97 xk8 convertible. The problem seemed to start last November, after I had it undercoated with Rust Check. about a week later I attempted to use it and it started, ran a few seconds and died. It logged a Stability Control Failure, a gear fault and an engine fault. I eventually changed the battery after load testing the old one. It did not make a whole lot of difference. However I trickle charged the new one and was able to cancel the fault codes. This sequence of events has repeated itself several times. Today it did it again, so I tested the battery draw when it was shut off to see if it was draining the battery down. it appears ok. So then I tried to clean the ground in the trunk(boot) the two in the engine bay by the fuse busses and the ground strap at the starter. I still cannot get the fault codes to cancel. My OBDII scan tool keeps coming up with different numbers of faults every time I try to erase the se codes. Has it logged a hard code that a hand held scan tool won't erase? I am getting really frustrated with this seemingly on-going problem. Has anybody else experienced this??