Premiere Pro CS6 Playback Lag.

I'm expiriencing quite a lot of stuttering and lag when I play the video I'm editing in Premiere Pro. This only happens in one project that I have created. The playback resolution is set to half(1/2)  of 720x576(the Playback Resolution in Sequence Settings)

The playhead is moving but the image in the preview window is either stuck at one frame or it changes to a different frame after a few seconds. The video isn't too long, and it also doesn't have too many effects added. I would like to fix that. I've tried to change the rendering method to Software, but that only helped a bit. 

Some of the other fixes I have tried:

1. I changed the Pixel Aspect Ratio to 1.0(didn't help)

2. I also changed the Preview File Format to P2 DVCPRO50 NSTC, this didn't help a lot.

The version of Premiere is CS6 and the computer hardware specifications are:

Intel Xeon E3-1275 v2 3.5Ghz

16GB DDR3 RAM

NVIDIA GTX 560Ti 1GB GDDR5

(I assume that the PC is above the minimum requirements for Premiere CS6)