Hi hope this helps A500 plus Owners
The 500 plus has a Capacitor in between fat Agnus socket and rom chip Positioned at "c816" which stops the vampire board locating fully down in the cpu slot.
My solution to the problem was to replace the capacitor with a smaller one that will do the same job.
After replacing the capacitor, the board was resting on the rom chip ,so I removed it ,I read some where
you do not need the rom chip so left it empty, fitted the vampire board and it worked Perfectly.
rev5 and rev 6 motherboards do not have this problem. no Capacitor at that Location.
plus you my be Able to use some Risers on the CPU socket ,but this may put the vampire card in contact with the key board must admit I do not know.
please have a look at the pics
hope this helps