Another Setback

Today was a major setback. i went to the gym with a great workout planned and i could barely get through the first couple of exercises. My plan was to hit it hard with a vest on, cause a lot of the qualifiers have had wods with vests on. So here was the wod i was going to do: (with a 40# vest)
500m row
 5x
5 Pullups
5 Back Squats (225#)
5 Lateral Burpees
500m row
 4x
10 Pullups
10 Front Squats (185#)
10 Lateral Burpees
500m row
 3x
15 Pullups
15 Overhead Squats (95#)
15 Lateral Burpees

I could only get the first row, 5 pullups, and failed on the squats. My knee just couldn't handle the squats. I'm able to run with no pain, do box jumps, and any plyo stuff, and my knee feels great, but external weight kills!
So after i couldn't finish my wod, i just did  heavy strict shoulder presses. Ended up with 150 for 4 reps. Will fight this battle tomorrow!