I've done the same thing Russ has suggested, moved around when I get hung up. it helps. I'm finding the exercises near the end are easier for me than some of the middle ones for instance.
The real reason I'm posting though is I was thinking about something related to this a few days ago. I put the cd examples on itunes, and then I can set them to repeat, so I can play along and not have to keep hitting "replay" or whatever.
Anyway... one of the options in the software is a "play count" that tallys how many times a song has been played. It seems it takes me 50-75 times playing along on some of these to get somewhat comfy with them, and on Muddy 'A' Blues for example I'm at abotu 75 plays and still screw up each time I try to record.
Point being, it takes time. That's 75 times playing along, not counting the times I play it by myself, or the times I'm playin galong in Garage Band trying to record it.
Some of them come easier than others. And maybe "easy" isn't the right word for it but the first ones are more simple than some of the later stuff. But you'd expect that, right?
And if you put th etime in, it will get easy. I STRUGGLED with the B7 chord at first. Avoided practicing it. Thought it was really tough. Now it's not really any more difficult than most other chords.
It'll get better, you just need to keep at it. But... progress never gets truly easy. When a piece gets easy you'll just start working on something more complicated, and that's what makes you get better.