I usually move my shrubs in late winter or very early spring - usually March. They are still dormant but about ready to wake up.
Barberies are forgiving and easy to move, just watch out for the thorns. :-) I have 3 Berberis thunbergeii 'Helmond Pillar' that got moved 3 - 4 times each. "Royal Burgundy' also got moved. In fact, I moved some of them in spring. They all are doing well.

Good luck.

I agree with pit...

You may be interested in a reply I left to a post similar to yours recently:

Prepare for a spring transplanting by root-pruning now. Make intermittent cuts around the circumference of the tree in a circle about the size that will yield the largest root-ball you're comfortable moving. The object is to sever about half the existing roots so that fine, feeder roots will form on the severed roots close to the trunk so you can include them when you move the plant. This will lessen the shock of transplanting and speed re-establishment in its new site. Lift and transplant in spring as soon as frost goes out of the ground or about 2 weeks before you expect buds to move. Dig a hole larger in diameter than necessary. Plant with the basal flare exposed and backfill with native soil only.
If you know your soil, supply an appropriate fertilizer blend that's low in N. Tomato fertilizer is a good choice for fall feeding of trees or shrubs to be lifted soon.

Al