Adobe Flash embeds do not follow standard z-index visibility rules. You will need to set the wmode parameter to transparent to make CometChat appear in front of Flash objects/advertisements.

For example, look at the wmode parameters in this sample YouTube code:

<object width='425' height='344'> 
    <param name='movie' value='http://www.youtube.com/v/Ahg6qcgoay4'> 
    <param name='type' value='application/x-shockwave-flash'> 
    <param name='allowfullscreen' value='true'> 
    <param name='allowscriptaccess' value='always'> 
    <param name="wmode" value="transparent" />
    <embed width='425' height='344'
            src='http://www.youtube.com/v/Ahg6qcgoay4'
            type='application/x-shockwave-flash'
            allowfullscreen='true'
            allowscriptaccess='always'
            wmode="transparent"
    ></embed> 
    </object>

For more information, refer to the Adobe article on Transparent background in a SWF file.