When you started making changes to the form (i.e.modifying collections), you may have broken the path to the elements. So if you renamed a subform from SubForm A to Subform B, and didn't update the path in the calculation script, then the form can't find the location of the element on the form, hence the error.
That could be one issue.
I'm not sure if you care able to attach files here anymore, but if you upload to Acrobat Workspace and share, I'll take a look. Our you can send to firstname.lastname@example.org and I'll gladly take a look.