PIC 18F242 not starting

[Evolution]

My circuit uses an 18F252 with 20MHz low profile crystal and 33nF capacitors for the clock. Power comes from a 7V bench supply, through a standard 7805 regulator and a MAX232 is used for serial to a PC. There are 100nF power line decoupling capacitors scattered on the board. My problem is that, on switch on, the PIC fails to start about 7 times out of 10. Also, the program often stops and the PIC re-starts at random. The same thing happens when the PIC sends instructions to a DAC.

Has anyone any experience of this problem and a suggested solution?

have you set you program option to hs oscillator??????????

[manxman]

Yes, the program has a header line defining this oscillator frequency. The problem is solved as described before.