A few years back this started showing up when Adobe entered into transparency in Illustrator. I think there was a reason transparency was left in Photoshop, but then was introduced in vector graphics and has been troublesome ever since. That said, it appears to be some sort of "stitching" going on in the preview or the file itself. I wonder if the file prints fine or you see the lines in a high res proof? There also could be some compression artifacts in play as well. It may require you to test a few different levels of compression in your .jpg's. Also, you might want to check your document raster effects resolution. Not sure where you plan on going with the file, but the higher the resolution, the better.
I think its not about CS5 but your image looks like it has some masks or effects so my suggestion what if you make it a raster before you slice it or check what happens when you save that slice to a different famat
original vector is 800x800, red is two objects - red and white 20% transparency (it's part of gass button)
when save jpg 2000x2000 it's fine
when save jpg 3000x3000 or biggest it have white lines
png, gif have some problem
Illustrator CS4 save this as jpg 8000x8000 fine
Maybe cs5 have new rasterization module?
Just try rasterize Edit->rasterize - new image have white lines
I have this exact issue.
Happens in "Save for web" and in "export". I managed to keep CS4 still installed and took the exact same file and "exported" it and "saved for web", and no issue at all in CS4. This is def. an issue that has popped back up in CS5 then.
On my attached image there is no gradients or special effects, just clipping masks.
I've tried the new options they have in save for web, "Art Optimized" and "Type Optimized". The issue does not happen in "Type Optimized" but the quality in type optimized is lower and it renders the exact same as the vector file appears(so colors bleeding out a pixel behind some objects etc.) The issue does happen in "art optimized".
Issues happens when saving in png and jpg format, with or without transparency.
I've attached an example, notice the lines in her face. (same as initial attached image)
So is this a "wait for an update" sort of scenario? or is this a "use a different program to save for web" scenario?