Follow the installation instructions carefully.

When a crank using external bearings binds it is usually because the faces on the BB shell on the frame are not parallel. This is - as mentioned - corrected by facing the shell. This can be achieved at home with the right touch, but take it to a shop to have it done correctly.

It can happen that you do not have binding in the original BB but do with a new one for a couple of different reasons. The original install may have been binding but you may not have noticed it because you didn't install it and as time went on the bearings wore out enough to no longer feel like it was binding. Also BB cups with tighter tollerancing seem to fit tighter. Probably a tighter interface with the crank spindle.

Also - not the first instalation difficulty I have heard of from a CK external BB. Recently a local pro cross rider almost missed out on his race because of installation trouble....resulting in having to chase and face the BB to solve.