Replacement foot doesn't fit right.
 

I have a Singer 99 and it came with a zipper foot on it. I ordered a low shank foot from Sew-Classic and when I attach it it doesn't really press down at all on the fabric enough to scoot the fabric across the feed dogs. I can pull the fabric right out from underneath the foot. Did I get a defective new foot? This is the one I purchased...

http://shop.sew-classic.com/Low-Shan...5321-45321.htm

Any ideas? Thank you in advance.

Have you tried adjusting the pressure on the presser foot?

Have you tried contacting Sew-Classic by email or phone to describe how the foot is acting on your machine, they should be able to guide your inquiry?
Don't know if this would apply beyond checking the pressure on your pressure foot, are your feed dogs up?

Yes, my feed dogs are up and everything works fine with the original zipper foot but not with that new replacement foot.

I have purchased many of those feet from Sew-Classic. What I've found is:
>They are basically of good quality.
>They are "similar" to the original Singer straight stitch feet, but not exact.
>If I check the foot height with a factory Singer SS foot, then put one of the new ones on I've always got less room under the new foot.
>When I've used the adjustable zipper feet I have much less room than when using a Singer straight stitch foot
>Sometimes the new straight stitch foot does not line up with the feed dogs like the OEM one does.

OK, here is what "might" be going on with your machine. Your presser foot shaft could be set too high. To find out for sure you'll need to remove the needle and rotate the hand wheel till the feed dogs are below the needle plate.
Then lower the presser foot. It should sit directly on top of the needle plate with a little bit of free play between the presser foot lift lever and the presser foot lift part. This ensures the spring is putting full pressure on the foot, not the lever.
If there is any clearance then you will have the condition you describe. When the feed dogs rotate down there is no pressure on the fabric and you can pull it right out.

On every Singer 66 and 99 (every other machine for that mater ) that sews nicely the presser foot sits directly on the needle plate when the feed dogs are down. It is one of the first things I check on a new to me machine. I keep a Singer OEM SS foot handy to set them with if needed.

Joe