PIC resets every now and then

[passion1]

My pic 16F73 resets every now and then.
I am using a 20MHz external crystal with 2 x 22 pf capacitors.
I also have a 10K resistor between between MCLR and +5V.
Even if I scale down my program to a few lines consisting only of output to the LCD, my pic still resets every now and then.
I have followed Darren Taylors advice and have sent the output of the
POR, BOR, TO and PD bits to the LCD just after initialization, as to help to determine what cause the resets.
The values after each reset is as follow:
POR=0 (Power-On reset PCON.1)
BOR=0 (Brown-out reset PCON.0)
TO=1 (Time-out bit STATUS.4)
PD=1 (Power-down bit STATUS.3)

Using the above values as a clue, what could be the problem?
Accortding to the datasheet, POR=0, BOR=unknown, TO=1, PD=1 indicates it was a Power-on-reset.
This doesnot make sense. How can a Power-on reset happen 10-30 seconds after startup?