Because you're hard coding the bolt name "Bolt_01" but when you rename you are renaming "nut_01" What you need to do is to capture the actual name generated with the import string $current_bolt = `file -import "E:/Bolt_01.ma"`; And use $current_bolt for move/constraint/etc.
Ok, I hacked that together. Currently, the renaming won't work if you have numbers in the name anywhere besides the end. http://www.sinistergfx.com/data/max/scripts/SGFX_MegaInstance.mcr I was going to just tell you to use Tools > Rename Objects; but I decided to give it a try.
Can anyone suggest a tool for unlocking files which you've had open in Photoshop, then want to rename/delete etc? That 'Cannot delete file it is being used by another person/program' message is becoming a real pain. I tried a prog called unlocker - which is a partial solution in that it will rename/delete files when you…