Browser Compatibility

[mac_designer]

Try fixing in the invalid markup first and see if that doesn't help - http://validator.w3.org/check?verbos...oducts_id%3D76

I could not find any additonal info in the threads addressing my problem...and I don't understand how to fix the invalid markup.
Is there a specific php or css file that I should be making adjustments to in order to fix the invalid markup?

Thanks