Nestopia Display Problem

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When using the Nanao 2933 monitor which is auto-switching, etc... I can plug it directly into my onboard video on my computer's motherboard and it works fine for pretty much everything.

However, when I run Nestopia, I get two images of the same screen - one on the left, one on the right.

I don't expect any Nestopia experts here, but does anyone know what causes this problem?  Is it refresh rate?  I figure there's some setting in Nestopia I need to make.  I can hook up my 19" lcd and it looks fine. 

I'm running 640x480 60hz

Thanks.

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Figured it out.  I had to uncheck the auto-set option under monitor frequency.