When you "duplicated the field" you put it in a new context (probably) and the previous relationships are, perhaps, not valid. When you mention "pull-down field" I assume you mean either a drop-down or pop-up and both are based on Value Lists, some of which may be "conditional". Best check out your relationships relevant to the Value Lists.
Also, from what version of FileMaker are you upgrading? If this was version 6 or older, there is some chance that the file conversion wasn't perfect and that additional changes need to be made to get it fully functional.