Problem screwing in motherboard screws

Hi guys I'm getting frustrated with my motherboard screw. I can't seem to screw it in, i've got the other 8 screwed in but this last one only goes in half way before it gets super tight then if I continue screwing the standoff starts to rotate as well! Could it be that I brought the standoffs from ebay and they're cheap or am I doing it wrong. The case is a Antec One and i'm not using the 6 incuded standoffs but rather the 8 (& 1 plastic thingy in place of the middle standoff!) I brought of ebay (and they're a bit longer than the originals)

Use the ones that come with the case, there's a reason for them.

There aren't enough standoffs for my ATX mobo though that's why I brought some from ebay! It's the bottom left screw and standoff which is causing the problem however I did stuggle screwing in the rest as well... I can tighten it but then the screw starts to rotate along with the standoff

The standoff is obviouslt slipping in the case. You've got a knackered screw hole in your case probably, there's nothing that you can really do.

But it doesn't really matter, the top screws are the most important ones. You could just leave it out and it will be fine.

Okay so i've managed to screw them all in but i'm using 4 tall standoffs and 3 shortER ones is that bad, will the motherboard warp (not that I can see any flexing!?

use the standoffs from antec. 6 will hold the mobo just fine. 2 top, 2 middle, 2 bottom. and they all need to be same size... your mobo isnt made for flexing.

Installed it and it's up and running Now :)so so good, btw I grabbed some decent Standoffs from Maplin (UK pc part supplier) and these ones are doing the job great