Access 2010-2016 Compatibility Error
Community wiki answer:

That particular error message is the key:


  Compile error: cannot find  project or library


Opening the office 2010 database in 2016 removed all of the VBA references to 14.0 Object Libraries in the References menu, and replaced them with 16.0, which is not present in Office 2010.

Broken references are to be expected when the .mdb is opened in an older version. It happens when there are references to Office libraries (Word, Excel, etc). Edit the references (in the VB Editor) in the oldest version (the one that doesn't run the code).