I am using the circuit according AN 461 page 12, but with Vpp connect to a capacitor an resitance as state in the errata.
Mistype or mistake?
Vpp must be connected DIRCTLY to Vcc, if I remember correctly, the RC is for !PSEN.

Another possibility is that in 6 clk mode the Rx2 can only run to 20MHz are you using a higher freq which will work to 33MHz in 12 clk mode?

Erik