Masked LCD

I've started on a LCD project. I’m using a 4 line by 20 char LCD,MDLS-20464-SS-LV-G, and I get a screen filled with all dots. When I unplug the VO connection to the LCD, and then plug it back in- just as I plug it back in I see the “Select 1” message and then it goes to all dots. I can do this repeatedly. It’s like the message is being masked. It also displays the message temporally when the circuit is powered down. What could be the problem?

Thanks in advance,

1.poor and/ or noisy power-supply
2.Use of Analog i/o
3.Use open drain i/o
4.Vo pot value too high
5.I hear that some LCD in 4 bit mode may need to have their unused DBx line to Vss OR Vcc.
6.Aliens

I found that Vo was to high. I placed a variable resistor between Vo and ground and was able to see the display fine. So you were right abt Vo.