Hi there,
Please check the complete version of Captivate 6 (help > about adobe captivate), it should be 6.0.1.240 or 6.1.0.319.
Select a slide and in the properties of that slide, increase the quality to 24 bit or optimized. Now, do this for every slide.
Then go to Edit> Preferences > SWF size and quality, make that to custom and uncheck Advanced Project Compression, uncheck Compress full motion swf file and uncheck Compress SWF file.
Then publish and at the time of publishing 'force republish all slides should be checked'
Thanks.