Greg, sometimes the locktite product they use takes a stronger hold on some weights vs. others.  I would consider sending it back to custom shop or if you feel brave you can use a torque wrench with a weight removal tool from Scottycameron.com and it will probably come undone with some effort. 

Just some random thoughts, I have removed and exchanged weights hundreds of times over the years and both options work fine.

Good Luck!