Illustrator CS6 Gaussian Blur Effect on a object that is set in a Pantone Spot Color results in halo effect.
If we change the Pantone Spot Color to Process, the effect is as we would expect, but need to use spot colors for output to press.
The Feather Effect is a possible replacement for the Gaussian Blur when spot colors are used but requires resizing of the object to match design.
Is there a fix or workaround to allow us to use spot colors and new Gaussian Blur effect together as we did in Illustrator CS5?
Gaussian blur does not resize when you scale, so rebuilding using the feather effect may be worth the effort.
Without a screenshot, hard to nail down exactly what this is coming from. You may be having a transparency flattener problem. Print >> Advanced >> Custom >> move slider towards raster.