Jimbo_Bimbo

I thought I knew what i was doing with chain adjustment, but I've just adjusted my chain and i'm getting a tight spot when i rotate the back wheel. When i put the new chain on etc i slacked the adjustor bolts right back and pushed the wheel forward and then slowly (soooo slooowly) adjusted it evenly of each side so that the chain was the right tension. Its been fine until the recent adjustment. The chain is well lubricated witha Scottoiler.
Could it be just that its out of alignment or something more sinister?

Thanks
Jim