Rear wheel not spinning when the skewer is locked in Can someone please tell me what is causing my rear wheel to "stiff up" when pedaling. I recently cleaned the rear hub because at first it was causing the wheel to "stiff up" when pedaling.

At first I thought dirt and grime were causing the problem. So I cleaned it and it still does the same thing.

The axle or skewer are not bent. The cassette rotates back and forth however I have noticed that when I lock on the skewer it causes the wheel to stiff up. I don't know what to do anymore and its becoming frustrating.
When you cleaned the rear hub, did you reassemble it in the right order?   Sounds like your axle is too far over, or there's possible a lock nut in the wrong place, so that when you cinch down the QR, the dropouts are touching the axle (OK) and the wheel hub (not OK)

If the wheel spins okay on its axle/bearings when off the bike, then something about fitting is making it bind.  Check your brakes and both the chainstay and seatstay clearance points when the wheel is fitted.  Hang the bike up and slowly spin the wheel looking at each point to see if the wheel is rubbing at some point - it may be out of true.